An anti-siphoning device for use in the tubular fuel filling neck of a vehicle such as a large truck includes a tubular body, which is mounted in the filling neck, resilient fingers on the body for resisting removal of the body from the neck, a plate in the body with a central opening for receiving a fuel dispensing nozzle, vent openings in the plate around the central opening for discharging gases from the fuel tank during a filling operation, a tube extending downwardly from the central opening, and a cage on the bottom end of the tube for preventing insertion of a siphoning tube into the tank.