An improved kingpin locking system includes a kingpin lock body having upper and lower sections, the lower and upper section each having a truncated generally pyramidal shape, with the lower one being inverted, a central kingpin-receiving chamber formed in the kingpin lock body, a kingpin engagement bar movably mounted in the kingpin lock body adjacent the kingpin-receiving chamber which releasably engages the kingpin when positioned within the chamber, and a kingpin engagement bar locking device which releasably locks the kingpin engagement bar in the engagement position thereby releasably securing the kingpin lock body on a kingpin to prevent unauthorized engagement of the kingpin and thereby preventing unauthorized use of the trailer.