The KVM garbage collector implemented in CLDC was generally based on the simple mark-sweep algorithm, but it is difficult to handle objects of varying size without fragmentation of the available memory. In this paper, we have designed and implemented a memory allocator based on the mark-sweep algorithm that minimizes the fragmentation by the method that determines the allocation position of free-space list according to object size. The experimental result shows that our algorithm reduce the fragmentation and improve the execution time than the existing algorithm.