In the search for antioxidants from microbial organisms, we found that Penicillium roquefortii IFO 5956 produced an antioxidant. This antioxidant was isolated from a culture broth of the strain, and its structure was identified to be 2, 3-dihydroxy benzoic acid (1). The antioxidative activity of 1 was nearly equal to that of tert-butyl-4-hydroxyanisol(BHA).