A semiconductor memory device and a memory system including the same are provided. The semiconductor memory device may include a first memory cell array block generating first data, a second memory cell array block generating second data, and first and second error detection code generators. The first error detection code generator may generate a first error detection code and may combine a portion of bits of the first error detection code with a portion of bits of a second error detection code to generate a first final error detection signal. The second error detection code generator may generate the second error detection code and may combine the remaining bits other than the portion of bits of the second error detection code with the remaining bits other than the portion of bits of the first error detection code to generate a second final error detection signal.