A memory device that checks an error of a memory cell and a memory module including the same are disclosed. The memory module includes a first memory device and a second memory device. The first memory device includes a first area in which normal data are stored, and a second area in which error check data are stored. The second memory device stores reliability information about the normal data that is stored in the first area of the first memory device. The first memory device outputs a result of comparing the normal data read from the first area of the first memory device to the error check data read from the second area of the first memory device.