Page buffer and programming method of a non-volatile memory device

A page buffer includes a first ground voltage supply unit for applying a ground voltage to first and second registers according to a level of a sense node, and a second ground voltage supply unit for applying the ground voltage to the first and second registers irrespective of a level of the sense node. A method of programming a non-volatile memory device includes storing a high-level data in a first node of a first register of a plurality of page buffers, precharging a sense node with a high level, resetting the data stored in the first node of the first register according to a voltage level of the sense node, precharging the sense node with a high level, storing external data in the first node according to a voltage level of the sense node, and performing a program operation according to the data stored in the first node.