A padlock includes a housing, a shackle, a limit knob, a movable block and a lock core. The housing has an opening in a wall thereof. The shackle has a shaft portion movably mounted in the housing, and a locking portion extended from the shaft portion and located outside of the housing. The limit knob is partly received in the housing via the opening and has a button located outside of the housing. The movable block is disposed on the limit knob and capable of moving to a predetermined position which is outside of the housing. The lock core has a rotor configured to be driven by a key so as to move the limit knob to a first position where the button of the limit knob keeps the shackle from rotating and a second position where the button of the limit knob allows the shackle to rotate.