A method of programming a nonvolatile memory device comprises counting a number of state pairs in a unit of input data, modulating the unit of input data to reduce the number of state pairs contained therein, and programming the modulated unit of input data in the nonvolatile memory device. Each state pair comprises data with a first state and designated for programming in a memory cell connected to a first word line, and data with a second state and designated for programming in a memory cell connected to a second word line adjacent to the first word line. The memory cell connected to the first word line is adjacent to the memory cell connected to the second word line.