An air pressure abnormality determination system determines whether an air pressure abnormality in which an air pressure of at least one of multiple front tires and multiple rear tires drops. The front tires are front wheels of a vehicle. The rear tires are rear wheels of the vehicle and of which outer diameter is different from an outer diameter of the front tires. A determination is made on whether the air pressure abnormality occurs using a corrected wheel speed obtained by correcting one of a front wheel speed that is a wheel speed of the front wheels and a rear wheel speed that is a wheel speed of the rear wheels based on the outer diameter of the front tires and the outer diameter of the rear tires and an uncorrected wheel speed that is the other of the front wheel speed and the rear wheel speed that is uncorrected.