A memory system includes a nonvolatile memory including memory cells, and a memory controller. The memory controller is configured to read first data through application of a first read voltage to each of the memory cells, perform a first decoding process with respect to the first data, when the first decoding process fails, perform a tracking process. The tracking process includes reading second data indicating a threshold voltage level of each of the memory cells through application of a plurality of second read voltages to each of the memory cells, and obtaining, with respect to each of the memory cells, likelihood information using the second data. The second read voltages are shifted by a predetermined amount. The memory controller is further configured to perform a second decoding process with respect to the second data using the likelihood information.