A method is provided for erasing a nonvolatile memory device, including multiple memory blocks formed in a direction perpendicular to a substrate, each memory block having multiple strings connected to a bit line. The method includes selecting a memory block to be erased using a power supply voltage; unselecting a remaining memory block, other than the selected memory block, using a negative voltage; setting a bias condition to reduce leakage currents of the unselected memory block; and performing an erase operation on the selected memory block.