Provided are memory devices and read level controlling methods. A memory device may include: a memory cell array that includes a plurality of memory cells; a counter that counts a number of memory cells with a threshold voltage included in a reference threshold voltage interval among the plurality of memory cells; a first decision unit that compares the counted number of memory cells with a threshold value to thereby decide whether to set a read level based on the reference threshold voltage interval; and a second decision unit that generates a new reference threshold voltage interval based on the comparison result between the counted number of memory cells and the threshold value.