A nonvolatile memory device and a programming method thereof perform a programming verification step including a selective verification step and a sequential verification step. In the selective verification step, a data input/output (I/O) circuit selectively precharges a selected bit line according to a temporary programmed state of stored data. In the sequential verification step, the data I/O circuit selectively precharges each bit line according to the result of the previous selective verification step or a previous sequential verification step. According to the programming method, because a memory cell not requiring a programming verification step is not precharged in the programming verification step, an ON cell current does not flow therethrough. Accordingly, the current flowing through a common source line during verification can be reduced.