According to example embodiments, an operation method of a nonvolatile memory device includes determining a location of a selected word line among word lines connected to the nonvolatile memory device, selecting one of a plurality of different read disturbance reducing modes according to the location of the selected word line, and performing a read or verification operation according to the selected read disturbance reducing modes. The nonvolatile memory device includes cell strings. Each one of the cell strings includes memory cells stacked on top of each other in a direction perpendicular to the substrate and between a ground select transistor and a string select transistor. The ground select transistor is between the substrate and the number of the memory cells. The string select transistor is connected to a bit line and is between the bit line and the number of the memory cells.