A data access method, a memory control circuit unit and a memory storage device are provided. The method includes generating a first error correction code corresponding to received first data according to a first error correction encoding operation; and generating a second error correction code corresponding to received second data according to a second error correction encoding operation, wherein the second error correction code includes a first and a second partial error correction code. The method further includes writing the first data, the first error correction code and the second partial error correction code to a data bit area and a redundant bit area of a first physical programming unit respectively; and writing the second data and the first partial error correction code to the data bit area and the redundant bit area of a second physical programming unit respectively.