According to one embodiment, a memory system includes a non-volatile memory and a memory controller that controls the non-volatile memory. The non-volatile memory includes a memory cell array and an access control unit. The access control unit performs a program operation for changing threshold voltages of memory cells and a read operation for reading data from the memory cells. The memory controller includes a read/write control unit having a first program parameter set and a second program parameter set. The read/write control unit causes the access control unit to perform a program operation based on the first program parameter set, and when a predetermined condition is satisfied, performs switching from the first program parameter set to the second program parameter set and causes the access control unit to perform a program operation based on the second program parameter set.