According to one embodiment, a memory system includes a nonvolatile memory, a random access memory and a controller. When writing n−1 data portions of a first unit that are included in n−1 error correction code frames of a first size, respectively, in the nonvolatile memory, the controller generates a second error correction code that constitutes an error correction code frame of a second size together with the n−1 data portions of the first unit and a second data portion to be written into the nonvolatile memory by encoding the n−1 data portions of the first unit and the second data portion, and writes the second data portion and the second error correction code into the nonvolatile memory.