Disclosed is a memory system including a memory device including a plurality of memory blocks; and a controller suitable for performing a garbage collection operation by: moving, when a first victim block related to map data stored in an external device is included in a plurality of victim blocks selected from the plurality of memory blocks, one or more pieces of valid data from the first victim block to a temporary block, which is a free block among the plurality of memory blocks, erasing the first victim block to set the first victim block as a first target block, and moving first valid data, which correspond to the map data stored in the external device among the valid data, from the temporary block to an original location within the first target block, wherein the first valid data is originally stored in the original location before the garbage collection operation.