A memory system includes a nonvolatile memory device, and a memory controller configured to control the nonvolatile memory device such that memory cells connected with a selected row of the nonvolatile memory device are programmed by one of a first program mode and a second program mode. At the first program mode, a plurality of logical pages corresponding in number to a maximum page number is stored at the memory cells, and at the second program mode, one or more logical pages the number of which is less than the maximum page number are stored at the memory cells using a bias condition that is different from that used in the first program mode.