Abstract: A door lock includes an external locking unit and an internal locking unit mounted on the door body of a door at outer and inner sides to hold a lock cylinder, and a locking bolt unit controlled by the external locking unit to lock/unlock the door, the internal locking unit having a circular base block fixedly fastened to the door body, a rotary cover rotatably mounted on the circular base block, a shaft forced by a spring member into engagement with the spindle of the lock cylinder, and a sliding knob mounted on the rotary cover and shifted between a first position wherein the rotary cover and the spindle of the lock cylinder are stopped from rotary motion, and a second position where the rotary cover and the spindle of the lock cylinder are allowed to be rotated between the locking position and the unlocking position.