A page buffer and method of programming and reading a memory are provided. The page buffer includes a first latch, a second latch, a data change unit and a program control unit. The first latch includes a first terminal for loading data of the lower page and the upper page. The second latch includes a first terminal for storing the data of the lower page and the upper page from the first latch. The data change unit is coupled to a second terminal of the first latch for changing a voltage of the second terminal of the first latch to a low level. The program control unit is coupled to the first terminal of the second latch and the cells, and controlled by the voltage of the first terminal of the first latch for respectively programming the data of the lower page and the upper page to a target cell.