Effects of culture pH ranging from pH 3.0 to 6.0 on yields of bioactive compounds, antioxidant activity, and free radical scavenging ability of methanolic extracts from mycelia and filtrates of Antrodia camphorata in a submerged culture were investigated. Culture pH significantly affected antioxidant and scavenging free radical activities of both the methanolic extracts of the mycelia and the filtrates. A low culture pH (3.0) favored cell growth, but higher culture pH (5.0) favored antioxidant properties. Antioxidant activities of the methanolic extracts of the mycelia and the filtrates were found to be correlated with total phenolic content, polysaccharide content, and protem/polysaccharide ratios. Antioxidant production was maximum at pH 5.0 at which the total phenolics and polysaccharide/protein ratio in the methanolic extracts of the mycelia were 152.2 mg/g and 0.335, respectively. The total phenolics might be the compounds responsible for the antioxidant activities of the methanolic extracts of the mycelia and the filtrates on lipid peroxidation and scavenging effects of ferrous ions. The maximum polysaccharide content of the methanolic extracts of the filtrates was 55.3 mg/g at pH 5.0. Higher yields of antioxidants were obtained in the submerged culture as compared with that of fruiting bodies. An alternative approach for producing antioxidants of A. camphorata in a submerged culture instead of solid state cultures was demonstrated in this study. (C) 2007 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.