According to one embodiment, a memory system includes a nonvolatile first memory, a volatile second memory, a capacitor, and a memory controller. The nonvolatile first memory includes a storage region that includes a plurality of memory cells. The capacitor is configured to accumulate electric power. The memory controller writes first data stored in the volatile second memory to the storage region in a first mode, using a power supply from outside. The first mode is a mode in which one-bit data is written to each of the memory cells. The memory controller writes, upon stop of the power supply from the outside, the first data to the storage region in a second mode, using the electric power accumulated in the capacitor. The second mode is a mode in which one-bit data is written to each of the memory cells and is different from the first mode.