Tannin acyl hydrolase (EC 3.1.1.20) or tannase is an enzyme which hydrolases the ester and depside bonds of hydrolysable tannin and gallic acid esters. Tannase had been studied in increasing antioxidant activity of several beverages. This research designed to study the effect of tannase addition to green tea and black tea in several pH conditions.Tannase was extracted from solid state culture of Aspergillus niger with three different fermentation time (24, 48,72 hours). Tannase was extracted by stirring and the protein was precipitatedwith solid ammonium sulphate. The precipitate is suspended in distilled water and used as crude tannase. Tannase produced by 72 hours fermentation showed highest activity (422.3196 Unit/mg enzyme.minute). Tannase with highest activity was used for biotransformation and antioxidant activities of both samples were increased by tannase treatment. The antioxidant activity of green tea increased 87.849 % by biotransformation at pH 4.5 and 5.0 and 87.108 % increasing in black tea biotrasnformed at pH 6.0. Tannin content and Liquid Chromatography-Mass Spectroscopy was used for confirmation of tannase activity in both samples.