A memory system, a memory controller and an operating method are disclosed. By inputting a read command to the memory device, starting to input data for a write command when the write command is input to the memory device while the memory device performs a read sensing operation for the read command, and inputting, to the memory device, data for the write command when input of the write command is started, it is possible to enhance the write performance of the memory system when the memory system executes a write operation after a read operation.