An occupant protection system includes a seatbelt device mountable on a vehicle seat and an airbag device mountable in a vicinity of a fastening area of the seatbelt device where a buckle section of the seatbelt device buckles a tongue. The airbag device includes an airbag inflatable between a lap belt, a shoulder belt and an occupant seated in the seat. The airbag includes a front inflatable section extending forward and a rear inflatable section extending rear- and upwardly. The rear inflatable section is so configured as to ride over a vicinity of the fastening area and contact the front inflatable section when an occupant of the vehicle moves forward and pushes the rear inflatable section at an impact on a vehicle from the front of the buckle section.