A memory system may include a nonvolatile memory device and a wear leveling unit. The nonvolatile memory device includes a plurality of memory blocks. The wear leveling unit may be configured to intermittently increase an accumulative access count of a memory block among the memory blocks by a predetermined value, decide a wear level of the memory block based on the accumulative access count whenever the accumulative access count is increased, set the memory block to a hot block based on the wear level, and perform a hot block management operation on the hot block. The wear leveling unit may increase the accumulative access count in response to an access count reaching a predetermined value. The accumulative access count may be stored in the nonvolatile memory device, and the access count may be stored in a volatile memory device.