An anti-theft fastener with locking feature, comprising: a nut having therein a concave chamber and having an end provided with a flange, the concave chamber having therein an inner screw hole extending to and being in communication with an outer end of the flange, characterized in that at least a position-limiting hole is disposed on the external wall surface of the nut and communicates with the concave chamber of the nut, the at least a position-limiting hole having therein a positioning ball, wherein at least a receiving groove is disposed on an outer end side of the concave chamber of the nut, wherein a spring and an ejecting pin are disposed in the receiving groove of the nut; a ring disposed around the flange of the nut; a nut casing enclosing the nut, the nut casing having therein a receiving chamber and a receiving channel, wherein an engaging groove is disposed between the receiving channel and the receiving chamber of the nut casing, wherein at least a positioning engaging passage is disposed in the receiving chamber of the nut casing and corresponds in position to the positioning ball of the nut, wherein a through hole is disposed at an outer end of the receiving channel of the nut casing; a lock casing disposed in the receiving channel of the nut casing, wherein a press portion is disposed at an end of the lock casing and inserted into the through hole of the nut casing, the lock casing having therein a receiving chamber, the press portion having a through hole passing through the receiving chamber of the lock casing, wherein a guide groove is disposed on an inner wall surface of the receiving chamber of the lock casing, wherein at least a pin hole and at least a position-limiting hole are disposed on a wall surface of the lock casing, the at least a pin hole having therein a fixing pin, the at least a position-limiting hole having therein an engaging ball; and a lock disposed in the receiving chamber of the lock casing and having an annular groove, wherein a guide strip and at least a curved groove are disposed on a wall surface of the lock, the guide strip being disposed in the guide groove of the lock casing, wherein an abutting portion is disposed at an end of the lock. a nut having therein a concave chamber and having an end provided with a flange, the concave chamber having therein an inner screw hole extending to and being in communication with an outer end of the flange, characterized in that at least a position-limiting hole is disposed on the external wall surface of the nut and communicates with the concave chamber of the nut, the at least a position-limiting hole having therein a positioning ball, wherein at least a receiving groove is disposed on an outer end side of the concave chamber of the nut, wherein a spring and an ejecting pin are disposed in the receiving groove of the nut; a ring disposed around the flange of the nut; a nut casing enclosing the nut, the nut casing having therein a receiving chamber and a receiving channel, wherein an engaging groove is disposed between the receiving channel and the receiving chamber of the nut casing, wherein at least a positioning engaging passage is disposed in the receiving chamber of the nut casing and corresponds in position to the positioning ball of the nut, wherein a through hole is disposed at an outer end of the receiving channel of the nut casing; a lock casing disposed in the receiving channel of the nut casing, wherein a press portion is disposed at an end of the lock casing and inserted into the through hole of the nut casing, the lock casing having therein a receiving chamber, the press portion having a through hole passing through the receiving chamber of the lock casing, wherein a guide groove is disposed on an inner wall surface of the receiving chamber of the lock casing, wherein at least a pin hole and at least a position-limiting hole are disposed on a wall surface of the lock casing, the at least a pin hole having therein a fixing pin, the at least a position-limiting hole having therein an engaging ball; and a lock disposed in the receiving chamber of the lock casing and having an annular groove, wherein a guide strip and at least a curved groove are disposed on a wall surface of the lock, the guide strip being disposed in the guide groove of the lock casing, wherein an abutting portion is disposed at an end of the lock.