A method for locking data of a program memory embedded in a microcontroller is provided. The method keeps the data stored in the program memory from being dumped. The program memory consists of a one-time-programmable read only memory and is configured into a plurality of storage sectors. The method, according to the present invention, first receives a lock command in which the lock command corresponds to a specific storage sector of the program memory. Next, according to the lock command, which storage sector is the specific sector is recognized. Finally, an access lock module is activated for locking the specific storage sector.