Broussonetia papyrifera radix, fruits, leaves, and stems exhibit antioxidant, antinociceptive, antityrosinase, anti-inflammatory, and antiplatelet activities. However, study of the antioxidant activity of stem bark has been limited. In this work the antioxidant activity of stem bark and wood extracts were compared using different methods, and their phenolic constituents were analyzed. The bark ethyl acetate fraction exhibited the highest 2,2-diphenyl-2-picrylhydrazyl hydrate (DPPH) radical, hydroxyl radical scavenging activity, and the highest total phenolic and flavonoid contents. Both bark and wood n-butanol fractions showed stronger superoxide anion radical scavenging activity and reducing potential than other fractions. The bark and wood hexane fraction provided the highest level of ion chelating power. The high performance liquid chromatography (HPLC) analysis reveals there are more phenolic compounds in bark than in wood. These findings suggest that bark exhibits a higher antioxidant capacity than wood and that ethyl acetate and n-butanol fractions of B. papyrifera bark are potential natural resources for pharmacology of functional foods.