A memory storage device, a memory controller thereof, and a method for responding host commands are provided. The memory storage device has a flash memory chip and a buffer memory. The present method includes receiving a write command issued by a host system and determining whether the write command causes the memory storage device to trigger a data moving procedure. If the write command does not cause the memory storage device to trigger the data moving procedure, the present method further includes sending an acknowledgement message corresponding to the write command to the host system after data corresponding to the write command is completely transferred to the buffer memory.