We demonstrated that a dietary supplement, Antioxidant Biofactor (AOB®), a fermented grain food, inhibits phorbol ester (TPA)-induced inflammatory responses. Pretreatment of mouse skin with ethyl acetate extract of AOB (0.5mg) significantly attenuated the hydrogen peroxide level in mouse skin without inhibition of edema formation. Also, exposure of AOB extract to differentiated HL-60 cells resulted in dose-dependent inhibition of TPA-induced superoxide generation, which was stronger than those of the raw materials of AOB. Our results suggest that AOB is effective for prevention of skin oxidative stress.