A memory system includes a memory device and a memory controller. The memory device includes a memory cell array including normal memory cells and redundancy memory cells suitable for replacing failed memory cell among the normal memory cells, and a device controller for activating reserved memory cells which are included in the redundancy memory cells and not used to replace the failed memory cell. The memory controller controls the memory device, when a first memory cells are accessed more than a threshold access number, to move data stored in the first memory cells to the reserved memory cells and replace the first memory cells with the reserved memory cells.