A semiconductor memory device which stores refresh period information thereby adjusting a refresh period and a method of operating the same. The semiconductor memory device includes a cell array and a refresh information storing unit. The cell array includes one or more cell regions each having a plurality of memory cells. The refresh information storing unit is configured to store first information including a first refresh period and second information including a second refresh period in correspondence to each of the cell regions. Memory cells included in each of the cell regions are refreshed at the first refresh period according to the first information in a first refresh time band and are refreshed at the second refresh period according to the second information in a second refresh time band.