Natto, the traditional fermented soybean in Japan, is rich in nattokinase and antioxidant activities. In this study, Arachis hypogaea (peanut) rich in unsaturated fatty acid was used for fermentation by Bacillus subtilis natto and its antioxidant activities were assayed. Peanut natto showed to be same level of nattokinase activity as those of black soybean natto and soybean natto. Content of total phenol and flavonoids in peanut natto water extract are 1.09 mg/mL and 1.24 mg/mL. The total antioxidant ability is 78.35% under concentration of 100 mg/mL and its DPPH scavenging activity is 88.53%, the reducing power is 0.52. Peanut natto is shown to be high potential in the development as a healthy food.