A memory system includes a semiconductor memory device and a memory controller. The semiconductor memory device includes a plurality of dynamic memory cells. The memory controller controls the semiconductor memory device. The memory controller applies an auto-refresh command to the semiconductor memory device at each refresh interval of the semiconductor memory device such that the semiconductor memory performs a refresh operation in a normal mode, and does not apply the auto-refresh command to the semiconductor memory device during a self-refresh interval in which the semiconductor memory performs a self-refresh operation. After the semiconductor memory device exits from the self-refresh interval, the memory controller adjusts an application of the auto-refresh command in the normal mode by reflecting information of the self-refresh interval.