Provided herein are semiconductor memory devices and operating methods thereof. A semiconductor memory device may include a memory cell array including a plurality of cell strings, and a peripheral circuit. The peripheral circuit may include a voltage generating unit configured to perform a program loop for alternately performing a program operation and a verification operation on the memory cell array. The peripheral circuit may include a control logic configured to control the voltage generating unit to perform the program loop. Wherein, in performing the program loop, a second pass voltage applied to an unselected word line adjacent to a selected word line among a plurality of word lines connected with the memory cell array is lower than a first pass voltage applied to a remaining unselected word line during the program operation.