An operation method of a memory device, having a plurality of memory cells, includes receiving a partial write command, which includes a partial write enable signal (PWE) and a plurality of mask signals, during a command/address input interval. A data strobe signal is received through a data strobe line after receiving the partial write command Data is received through a plurality of data lines in synchronization with the data strobe signal during a data input interval. A part of the data is stored in the plurality of memory cells based on the plurality of mask signals, in response to the partial write enable signal, during a data write interval.