Abstract: A locking method for system with OSD function is disclosed, which comprises;a procedure of waiting for the lock-function call; a procedure of storing and displaying the inputted secret code by using the OSD function when the lock-function is called; a prodecure of checking whether the system is in the locked state after the secret code input is completed; a procedure of storing the inputted secret code and locking the system if the system is not in locked state; a procedure of comparing the inputted secret code with the secret code already stored if the system is in locked state; a procedure of displaying error message by making use of the OSD function if the secret codes don't match each other; a procedure of unlocking the system if the secret codes match each other.The present locking method enables the system already having OSD function to lock itself without additional display unit by using the OSD function.