A memory controller includes a read operation controller, an error correction circuit, and a read voltage controller. The read operation controller controls a memory device to read pieces of data from a selected page of the memory device by read voltages having different levels. The error correction circuit determines fail bit numbers of the pieces of data. The read voltage controller selects a reference voltage variation from among voltage variations included in a first read voltage table, based on an erase write cycle count of the memory device, and a reference fail bit number indicating a largest fail bit number of the fail bit numbers, and adjusts a level of each of the read voltages based on the reference voltage variation and a ratio value of a corresponding one of the fail bit numbers to the reference fail bit number.