A memory system may include: a memory device including a plurality of memory blocks, each of the memory blocks including a plurality of pages; and a controller suitable for: storing user data corresponding to a write command, in the memory blocks; storing map data corresponding to the stored user data, in the memory blocks; determining entropies indicating amounts of the map data updated in the memory blocks which correspond to the stored user data; and selecting source memory blocks among the memory blocks, which correspond to the entropies.