A data storage device includes a nonvolatile memory having a plurality of first memory cells connected to a first word line and a plurality of second memory cells connected to a second word line. A memory controller divides first data to be programmed in the first memory cells into first and second data groups and divides second data to be programmed in the second memory cells into third and fourth data groups. The nonvolatile memory device performs a third program operation of the second data group and a fourth program operation of the fourth data group after sequentially performing a first program operation of the first data group and a second program operation of the third data group.