Provided are a nonvolatile memory device and a method of performing a sensing operation on the nonvolatile memory device. The nonvolatile memory device includes a control logic coupled to a memory cell array including strings. The control logic is configured to control a first weak-on voltage applied to an unselected string selection line and a second weak-on voltage applied to an unselected ground selection line during a setup interval of the sensing operation for sensing data from a selected string. The unselected string selection line and ground selection line are connected to a string selection transistor and a ground selection transistor, respectively, of a same unselected string. The selected string and the unselected string are connected to a same bit line. The first weak-on voltage and second weak-on voltage are respectively less than a threshold voltage of the string selection transistor and the ground selection transistor in the unselected string.