According to one embodiment, a memory controller includes an encoder, a randomizing circuit, and an interface. The encoder subjects first data received from an external device to error correction coding. The randomizing circuit randomizes second data output from the encoder. The interface transmits third data output from the randomizing circuit to a nonvolatile semiconductor memory and controls write/read of the nonvolatile semiconductor memory. The interface transmits data of a size larger than or equal to a size of a write unit of the nonvolatile semiconductor memory to the nonvolatile semiconductor memory in a write sequence.