A semiconductor memory device and an operating method thereof are provided. The semiconductor memory device includes: a memory cell array including a plurality of memory cells; and a peripheral circuit programming first, second, third, and fourth memory cells connected to one word line and successively arranged, among the plurality of memory cells, wherein the peripheral circuit is configured to program the first and fourth memory cells in a first interval and program the second and third memory cells in a second interval. A semiconductor memory device having enhanced performance characteristics and an operating method thereof are provided.