An air processing system of a fuel cell vehicle mounted with an integrated valve includes: the integrated valve attached to an air inlet and an air outlet formed integrally with a fuel cell stack and adjusting amounts of air introduced into and discharged from the fuel cell stack. The integrated valve is positioned at the shortest distance from the fuel cell stack, such that an amount of remaining oxygen that is to be consumed at the time of stopping start of a fuel cell vehicle is minimized. Therefore, corrosion of cathode carbon is decreased as compared with the related art, such that durability of the fuel cell vehicle is improved.