The utility model relates to a theftproof lock for a motorcycle, which is mainly composed of connecting pins [1], semicircular tiles [2], screw bolts [3], a main lock body [5], a key [7], a lock core [8], a lock core positioning pin [9], a secondary lock body [12], a lock bolt positioning pin [14], a lock bolt [16], a movable lock body [23], etc., wherein, the two semicircular tiles are respectively matched with the main lock body and the secondary lock body to form two sets of lock body mechanisms through respective connecting pins, and the two sets of lock body mechanisms are respectively and fixedly arranged on both sides of a front fork of the motorcycle by respective screw bolts; the lock core, the lock bolt, etc. are formed into a part, and a lock bolt radial groove is clamped into the lock bolt positioning pin after the part is inserted into the secondary lock body by penetrating through the main lock body and rotates at 90 DEG, and thereby, the locking and non-detachable theftproof purposes are realized. The utility model is suitable for being arranged on various man's motorcycles.