According to one embodiment, a memory system includes memory cells capable of having data written therein at different write levels. A memory controller is configured to detect first data of the memory cells, then apply a first voltage that is lower than a voltage used for writing the data to the plurality of memory cells, detect second data of the memory cells after the first voltage has been applied, and estimate a write level for the data written to the memory cells based on a comparison of the first data and the second data.