A vehicle occupant protection system includes a seat belt device and a knee bag device for protecting an occupant sitting on a seat of a vehicle. The protection system also includes a control unit for controlling the seat belt device and knee bag device based on a detection signal and a prediction signal from at least one of a device for detecting a state of the seat, a device for detecting whether the seat belt device is used, a device for predicting a collision, and a device for detecting a condition of an accident.