To provide an anti-theft lock structure for a saddle of a bicycle.

A clasping rod seat is attached to one end of a saddle post of the bicycle, and a screw rod with a connection part pierces through the clasping rod seat. The connection part of the screw rod can be stored in a recessed groove of a gear piece. A bolt is pivotally attached to a quick handle with the gear piece and a pivot hole of the connection part, and a nut is tightened to be connected to a clasping bolt seat. The saddle is positioned without a possibility of being loosened and a lock bolt of a lock core put inside the quick handle is combined with projecting teeth of the gear piece to form the forced engagement condition, so that the saddle can be speedily attached/ detached and the theft of the saddle can be prevented.