A memory device and a method for operating the same are provided. The memory device includes a substrate, a plurality of word lines, and a plurality of dummy word lines. The word lines and the dummy word lines are located on the substrate. At least one side of each dummy word line is adjacent to the word line. At least one word line and at least one dummy word line form a group. The method for operating the memory device includes the following. At least one group is selected, and the group is operated. A first operational voltage is applied to the word line of the group. A second operational voltage is applied to the dummy word line of the group.