A method and an apparatus for controlling to lock or unlock in the portable terminal having a transparent display that has two display surfaces and is capable of double-sided touch input and double-sided display is provided. The method includes activating the transparent display according to a lock state or an unlock state of the transparent display; displaying a lock or unlock area, which notifies whether a display surface is locked, in a preset area of at least one of display surfaces of the transparent display; and changing the lock state or the unlock state of the at least one of the display surfaces of the transparent display and displaying whether the changed state is the lock state or the unlock state in the lock or unlock area of the at least one display surface, when a touch input is received in the lock or unlock area.