A data storing method, a memory control circuit unit and a memory storage device are provided. The method includes the following. When the memory storage device is powered-on, it is determined whether a power loss state of the memory storage device matches an unexpected power loss state according to a power-off instruction. Data is written into a plurality of physical programming units using a single-page programming mode and not using a multi-page programming mode when it is determined that the power loss state matches the unexpected power loss state.