Provided herein is a memory controller for controlling a memory device. The memory controller includes a workload detector configured to determine a change in workload based on reception of a changed request from a host or a change in clock received from an external device, a device performance controller configured to determine, if the workload is determined as changed, read performance based on a ratio of a size of data output to the host to a size of data requested from the host every preset period and configured to output a read-look-ahead (RLA) command to the memory device based on the determined read performance, a buffer memory configured to store data read from the memory device in response to the RLA command and a memory size controller configured to control a size of the buffer memory. The RLA command instructs to output data which is frequently requested from the host.