diff --git a/src/multi_skiplist.c b/src/multi_skiplist.c
index 15cc32c..611f1a6 100644
--- a/src/multi_skiplist.c
+++ b/src/multi_skiplist.c
@@ -19,6 +19,7 @@
 
 int multi_skiplist_init_ex(MultiSkiplist *sl, const int level_count,
         multi_skiplist_compare_func compare_func,
+        multi_skiplist_free_func free_func,
         const int min_alloc_elements_once)
 {
     int bytes;
@@ -99,6 +100,7 @@ int multi_skiplist_init_ex(MultiSkiplist *sl, const int level_count,
 
     sl->level_count = level_count;
     sl->compare_func = compare_func;
+    sl->free_func = free_func;
 
     srand(time(NULL));
     return 0;
@@ -107,11 +109,31 @@ int multi_skiplist_init_ex(MultiSkiplist *sl, const int level_count,
 void multi_skiplist_destroy(MultiSkiplist *sl)
 {
     int i;
+    MultiSkiplistNode *node;
+    MultiSkiplistNode *deleted;
+    MultiSkiplistData *dataCurrent;
+    MultiSkiplistData *dataNode;
 
     if (sl->mblocks == NULL) {
         return;
     }
 
+    if (sl->free_func != NULL) {
+        node = sl->top->links[0];
+        while (node != sl->tail) {
+            deleted = node;
+            node = node->links[0];
+
+            dataCurrent = deleted->head;
+            while (dataCurrent != NULL) {
+                dataNode = dataCurrent;
+                dataCurrent = dataCurrent->next;
+
+                sl->free_func(dataNode->data);
+            }
+        }
+    }
+
     for (i=0; i<sl->level_count; i++) {
         fast_mblock_destroy(sl->mblocks + i);
     }
@@ -151,6 +173,15 @@ DONE:
     return found;
 }
 
+static inline void multi_skiplist_free_data_node(MultiSkiplist *sl,
+        MultiSkiplistData *dataNode)
+{
+    if (sl->free_func != NULL) {
+        sl->free_func(dataNode->data);
+    }
+    fast_mblock_free_object(&sl->data_mblock, dataNode);
+}
+
 static inline int multi_skiplist_get_level_index(MultiSkiplist *sl)
 {
     int i;
@@ -244,7 +275,8 @@ int multi_skiplist_do_delete(MultiSkiplist *sl, void *data,
         if (deleted->head->next != NULL) {
             dataNode = deleted->head;
             deleted->head = dataNode->next;
-            fast_mblock_free_object(&sl->data_mblock, dataNode);
+
+            multi_skiplist_free_data_node(sl, dataNode);
             *delete_count = 1;
             return 0;
         }
@@ -266,7 +298,7 @@ int multi_skiplist_do_delete(MultiSkiplist *sl, void *data,
         dataCurrent = dataCurrent->next;
 
         (*delete_count)++;
-        fast_mblock_free_object(&sl->data_mblock, dataNode);
+        multi_skiplist_free_data_node(sl, dataNode);
     }
 
     fast_mblock_free_object(sl->mblocks + level_index, deleted);
diff --git a/src/multi_skiplist.h b/src/multi_skiplist.h
index 30249e5..3ad5930 100644
--- a/src/multi_skiplist.h
+++ b/src/multi_skiplist.h
@@ -17,6 +17,7 @@
 #include "fast_mblock.h"
 
 typedef int (*multi_skiplist_compare_func)(const void *p1, const void *p2);
+typedef void (*multi_skiplist_free_func)(void *ptr);
 
 typedef struct multi_skiplist_data
 {
@@ -36,6 +37,7 @@ typedef struct multi_skiplist
     int level_count;
     int top_level_index;
     multi_skiplist_compare_func compare_func;
+    multi_skiplist_free_func free_func;
     struct fast_mblock_man data_mblock; //data node allocators
     struct fast_mblock_man *mblocks;  //node allocators
     MultiSkiplistNode *top;   //the top node
@@ -56,12 +58,13 @@ extern "C" {
 
 #define SKIPLIST_DEFAULT_MIN_ALLOC_ELEMENTS_ONCE 128
 
-#define multi_skiplist_init(sl, level_count, compare_func) \
-    multi_skiplist_init_ex(sl, level_count, compare_func,  \
+#define multi_skiplist_init(sl, level_count, compare_func, free_func) \
+    multi_skiplist_init_ex(sl, level_count, compare_func, free_func,  \
     SKIPLIST_DEFAULT_MIN_ALLOC_ELEMENTS_ONCE)
 
 int multi_skiplist_init_ex(MultiSkiplist *sl, const int level_count,
         multi_skiplist_compare_func compare_func,
+        multi_skiplist_free_func free_func,
         const int min_alloc_elements_once);
 
 void multi_skiplist_destroy(MultiSkiplist *sl);
diff --git a/src/skiplist.c b/src/skiplist.c
index 1377e67..bad230d 100644
--- a/src/skiplist.c
+++ b/src/skiplist.c
@@ -18,7 +18,8 @@
 #include "skiplist.h"
 
 int skiplist_init_ex(Skiplist *sl, const int level_count,
-        skiplist_compare_func compare_func, const int min_alloc_elements_once)
+        skiplist_compare_func compare_func, skiplist_free_func free_func,
+        const int min_alloc_elements_once)
 {
     int bytes;
     int element_size;
@@ -92,6 +93,7 @@ int skiplist_init_ex(Skiplist *sl, const int level_count,
 
     sl->level_count = level_count;
     sl->compare_func = compare_func;
+    sl->free_func = free_func;
 
     srand(time(NULL));
     return 0;
@@ -100,11 +102,22 @@ int skiplist_init_ex(Skiplist *sl, const int level_count,
 void skiplist_destroy(Skiplist *sl)
 {
     int i;
+    SkiplistNode *node;
+    SkiplistNode *deleted;
 
     if (sl->mblocks == NULL) {
         return;
     }
 
+    if (sl->free_func != NULL) {
+        node = sl->top->links[0];
+        while (node != sl->tail) {
+            deleted = node;
+            node = node->links[0];
+            sl->free_func(deleted->data);
+        }
+    }
+
     for (i=0; i<sl->level_count; i++) {
         fast_mblock_destroy(sl->mblocks + i);
     }
@@ -225,6 +238,9 @@ int skiplist_delete(Skiplist *sl, void *data)
 
     deleted->links[0]->prev = previous;
 
+    if (sl->free_func != NULL) {
+        sl->free_func(deleted->data);
+    }
     fast_mblock_free_object(sl->mblocks + level_index, deleted);
     return 0;
 }
diff --git a/src/skiplist.h b/src/skiplist.h
index 6ee80be..97bc942 100644
--- a/src/skiplist.h
+++ b/src/skiplist.h
@@ -17,6 +17,7 @@
 #include "fast_mblock.h"
 
 typedef int (*skiplist_compare_func)(const void *p1, const void *p2);
+typedef void (*skiplist_free_func)(void *ptr);
 
 typedef struct skiplist_node
 {
@@ -30,6 +31,7 @@ typedef struct skiplist
     int level_count;
     int top_level_index;
     skiplist_compare_func compare_func;
+    skiplist_free_func free_func;
     struct fast_mblock_man *mblocks;  //node allocators
     SkiplistNode *top;   //the top node
     SkiplistNode *tail;  //the tail node for interator
@@ -46,12 +48,13 @@ extern "C" {
 
 #define SKIPLIST_DEFAULT_MIN_ALLOC_ELEMENTS_ONCE 128
 
-#define skiplist_init(sl, level_count, compare_func) \
-    skiplist_init_ex(sl, level_count, compare_func,  \
+#define skiplist_init(sl, level_count, compare_func, free_func) \
+    skiplist_init_ex(sl, level_count, compare_func, free_func,  \
     SKIPLIST_DEFAULT_MIN_ALLOC_ELEMENTS_ONCE)
 
 int skiplist_init_ex(Skiplist *sl, const int level_count,
-        skiplist_compare_func compare_func, const int min_alloc_elements_once);
+        skiplist_compare_func compare_func, skiplist_free_func free_func,
+        const int min_alloc_elements_once);
 
 void skiplist_destroy(Skiplist *sl);
 
diff --git a/src/tests/test_multi_skiplist.c b/src/tests/test_multi_skiplist.c
index 64a8039..32a5bbc 100644
--- a/src/tests/test_multi_skiplist.c
+++ b/src/tests/test_multi_skiplist.c
@@ -10,14 +10,20 @@
 #include "logger.h"
 #include "shared_func.h"
 
-#define COUNT 12800
-#define LEVEL_COUNT 18
+#define COUNT 1000000
+#define LEVEL_COUNT 16
 #define MIN_ALLOC_ONCE  32
 #define LAST_INDEX (COUNT - 1)
 
 static int *numbers;
 static MultiSkiplist sl;
 static MultiSkiplistIterator iterator;
+static int instance_count = 0;
+
+static void free_test_func(void *ptr)
+{
+    instance_count--;
+}
 
 static int compare_func(const void *p1, const void *p2)
 {
@@ -32,12 +38,16 @@ static int test_insert()
     int64_t end_time;
     void *value;
 
+    instance_count = 0;
     start_time = get_current_time_ms();
     for (i=0; i<COUNT; i++) {
         if ((result=multi_skiplist_insert(&sl, numbers + i)) != 0) {
             return result;
         }
+        instance_count++;
     }
+    assert(instance_count == COUNT);
+
     end_time = get_current_time_ms();
     printf("insert time used: %"PRId64" ms\n", end_time - start_time);
 
@@ -74,6 +84,8 @@ static void test_delete()
     for (i=0; i<COUNT; i++) {
         assert(multi_skiplist_delete(&sl, numbers + i) == 0);
     }
+    assert(instance_count == 0);
+
     end_time = get_current_time_ms();
     printf("delete time used: %"PRId64" ms\n", end_time - start_time);
 
@@ -120,7 +132,9 @@ static int test_stable_sort()
     Record target;
     void *value;
 
-    result = multi_skiplist_init_ex(&sl, 12, compare_record, 128);
+    instance_count = 0;
+    result = multi_skiplist_init_ex(&sl, 12, compare_record,
+            free_test_func, 128);
     if (result != 0) {
         return result;
     }
@@ -142,7 +156,9 @@ static int test_stable_sort()
         if ((result=multi_skiplist_insert(&sl, records + i)) != 0) {
             return result;
         }
+        instance_count++; 
     }
+    assert(instance_count == RECORDS);
 
     for (i=0; i<RECORDS; i++) {
         value = multi_skiplist_find(&sl, records + i);
@@ -182,6 +198,7 @@ static int test_stable_sort()
                 (result != 0 && delete_count == 0));
     }
     assert(total_delete_count == RECORDS);
+    assert(instance_count == 0);
 
     i = 0;
     multi_skiplist_iterator(&sl, &iterator);
@@ -191,6 +208,8 @@ static int test_stable_sort()
     assert(i == 0);
 
     multi_skiplist_destroy(&sl);
+    assert(instance_count == 0);
+
     return 0;
 }
 
@@ -221,7 +240,8 @@ int main(int argc, char *argv[])
     }
 
     fast_mblock_manager_init();
-    result = multi_skiplist_init_ex(&sl, LEVEL_COUNT, compare_func, MIN_ALLOC_ONCE);
+    result = multi_skiplist_init_ex(&sl, LEVEL_COUNT, compare_func,
+            free_test_func, MIN_ALLOC_ONCE);
     if (result != 0) {
         return result;
     }
@@ -237,9 +257,13 @@ int main(int argc, char *argv[])
     test_insert();
     printf("\n");
 
+    /*
     test_delete();
     printf("\n");
+    */
+
     multi_skiplist_destroy(&sl);
+    assert(instance_count == 0);
 
     test_stable_sort();
 
diff --git a/src/tests/test_skiplist.c b/src/tests/test_skiplist.c
index 91bc728..412e9da 100644
--- a/src/tests/test_skiplist.c
+++ b/src/tests/test_skiplist.c
@@ -10,8 +10,8 @@
 #include "logger.h"
 #include "shared_func.h"
 
-#define COUNT 100000
-#define LEVEL_COUNT 18
+#define COUNT 1000000
+#define LEVEL_COUNT 16
 #define MIN_ALLOC_ONCE  32
 #define LAST_INDEX (COUNT - 1)
 
@@ -19,6 +19,13 @@ static int *numbers;
 static Skiplist sl;
 static SkiplistIterator iterator;
 
+static int instance_count = 0;
+
+static void free_test_func(void *ptr)
+{
+    instance_count--;
+}
+
 static int compare_func(const void *p1, const void *p2)
 {
     return *((int *)p1) - *((int *)p2);
@@ -32,12 +39,16 @@ static int test_insert()
     int64_t end_time;
     void *value;
 
+    instance_count = 0;
     start_time = get_current_time_ms();
     for (i=0; i<COUNT; i++) {
         if ((result=skiplist_insert(&sl, numbers + i)) != 0) {
             return result;
         }
+        instance_count++;
     }
+    assert(instance_count == COUNT);
+
     end_time = get_current_time_ms();
     printf("insert time used: %"PRId64" ms\n", end_time - start_time);
 
@@ -74,6 +85,8 @@ static void test_delete()
     for (i=0; i<COUNT; i++) {
         assert(skiplist_delete(&sl, numbers + i) == 0);
     }
+    assert(instance_count == 0);
+
     end_time = get_current_time_ms();
     printf("delete time used: %"PRId64" ms\n", end_time - start_time);
 
@@ -120,7 +133,9 @@ static int test_stable_sort()
     Record target;
     void *value;
 
-    result = skiplist_init_ex(&sl, 12, compare_record, 128);
+    instance_count = 0;
+    result = skiplist_init_ex(&sl, 12, compare_record,
+            free_test_func, 128);
     if (result != 0) {
         return result;
     }
@@ -142,7 +157,9 @@ static int test_stable_sort()
         if ((result=skiplist_insert(&sl, records + i)) != 0) {
             return result;
         }
+        instance_count++;
     }
+    assert(instance_count == RECORDS);
 
     for (i=0; i<RECORDS; i++) {
         value = skiplist_find(&sl, records + i);
@@ -182,6 +199,7 @@ static int test_stable_sort()
                 (result != 0 && delete_count == 0));
     }
     assert(total_delete_count == RECORDS);
+    assert(instance_count == 0);
 
     i = 0;
     skiplist_iterator(&sl, &iterator);
@@ -191,6 +209,8 @@ static int test_stable_sort()
     assert(i == 0);
 
     skiplist_destroy(&sl);
+    assert(instance_count == 0);
+
     return 0;
 }
 
@@ -221,7 +241,8 @@ int main(int argc, char *argv[])
     }
 
     fast_mblock_manager_init();
-    result = skiplist_init_ex(&sl, LEVEL_COUNT, compare_func, MIN_ALLOC_ONCE);
+    result = skiplist_init_ex(&sl, LEVEL_COUNT, compare_func,
+            free_test_func, MIN_ALLOC_ONCE);
     if (result != 0) {
         return result;
     }
@@ -233,14 +254,13 @@ int main(int argc, char *argv[])
 
     test_delete();
     printf("\n");
+    assert(instance_count == 0);
 
     test_insert();
     printf("\n");
 
-    test_delete();
-    printf("\n");
     skiplist_destroy(&sl);
-    fast_mblock_manager_stat_print(false);
+    assert(instance_count == 0);
 
     test_stable_sort();