A method of programming a nonvolatile memory device includes performing a single-pulse program operation in a program loop, determining whether a condition is satisfied in the a program loop, and performing a multi-pulse program operation in a next program loop when the condition is satisfied. The single-pulse program operation includes applying a first program pulse and applying plural verification pulses, the multi-pulse program operation includes applying a second program pulse, applying a third program pulse, and applying plural verification pulses, and each of the second program pulse and the third program pulse has a level lower than a level of the first program pulse.