A semiconductor memory device and a memory system are provided. The semiconductor memory device includes a memory cell array, a normal refresh row address generator, a hammer refresh row address generator, a refresh selection signal generator, and a selector. The normal and hammer refresh row address generators generates a normal refresh row address and a hammer refresh row address, respectively, in response to a refresh counting control signal. The refresh selection signal generator sequentially generates normal and hammer refresh selection signals in response to the refresh counting control signal. The selector selects the normal refresh row address or the hammer refresh row address in response to the normal and hammer refresh selection signals. A normal refresh operation and a hammer refresh operation are sequentially performed on a memory cell array block among plural memory cell array blocks in response to the refresh row address.