Abstract: A locking seat belt buckle assembly is configured for placement and operation within a standard seat belt buckle and tongue. In one embodiment, the seat belt buckle includes a latch that engages the tongue and a latch release plate to disengage the latch from the tongue upon depression of the release plate. The assembly includes a stop block that is movable by way of an actuator, such as a reversible micro-motor, to a position beneath the release plate to prevent depression of the latch plate. A pair of limit switches disconnect the motor from a power supply when contacted by the stop block at opposite ends of its travel. An indicator light is provided that is illuminated when the stop block is in position beneath the latch release plate. In one aspect, the motor is mounted within a housing with a spring disposed between the motor and the housing to bias the motor toward the release plate.