Tannase was found in the myceĩium of Aspergillus flavus grown on the medium containing tannic acid as a sole carbon source. The enzyme formation might be inducible and was dominant at the initial stage of growth.Tannase was purified about 30-fold from the mycelial extract of Aspergillus flavus grown on the tannic acid medium by a procedure involving ammonium sulfate and tannic acid precipitation, DEAE-cellulose column chromatography, Sephadex G-200 gel filtration and acetone fractionation. The final enzyme preparation showed single symmetric peak upon ultracentrifugation and electrophoresis.The enzyme was stable up to 60°C and showed optimum activity at 50 to 60°C. The optimal and stable pH ranges were found to be at 5.0 to 5.5 for methylgallate. The tannase of Aspergillus flavus hydrolyzed the ester linkages of tannic acid. The substrate- enzyme dissociation constants for substrates were found to be 0.5 × l0−4m, 1.4 × l0−4m and 8.6 × 10−4m for tannic acid, glucose-1-gallate and methylgallate, respectively.