According to one embodiment, a memory system includes a semiconductor memory and a memory controller. The memory controller writes a first data group in the semiconductor memory and then reads the first data group from the semiconductor memory. The memory controller counts a number of first data and a number of second data based on a comparison of a second data group with a third data group. The memory controller changes a first charge threshold based on the number of first data and the number of second data. The second data group is the first data group at the time of writing to the semiconductor memory. The third data group is the first data group read from the semiconductor memory. The first data is data changed from a first code to a second code. The second data is data changed from the second code to the first code.