A nonvolatile memory device includes a memory cell array and a row decoder. The memory cell array includes a plurality of mats. A first cell string of first mat is connected to a plurality of first word-lines, a first bit-line and a first string selection line. A second cell string of second mat is connected to a plurality of second word-lines, a second bit-line and a second string selection line. Each of the first and second cell strings includes a ground selection transistor, memory cells, and a string selection transistor coupled in series. The row decoder applies a first voltage to a third word-line among the plurality of first and second word-lines for a first period of time in a single mat mode and to apply a second voltage to the third word-line for a second period of time longer than the first period of time in a multi-mat mode.