A door lock includes an engaging member having a lock core hole. The lock core hole includes a large section and a small section. The large section is formed in an end of the engaging member that is detachably received in a shank of an outer handle. An interchangeable lock core is removably received in the large section. An end of an outer spindle is extended out of a lock body of the door lock and is detachably received in the small section of the lock core hole of the engaging member. The lock core has an outline corresponding to the large section of the engaging member. The lock core can be removed and replaced with a new one. The engaging member can be detached from the outer spindle and the outer handle and replaced with a new engaging member corresponding to the outline of the new lock core.