Tea is a popular beverage known to contain plenty phenolic and flavonoid compound, which usually associated as source of antioxidant for human body. During processing of oolong tea and black tea, these catechins are oxidized in presence of oxygen and polyphenol oxidase enzyme as catalyst. The polyphenol oxidase enzyme in banana also found to be able to oxidize catechins in tea but no further information were known about its effect on phenolic content, flavonoid content, and the antioxidant activity derived from those two compounds. This research is designed to study the oxidation of green tea extract at different pH (2.5, 3.5, 4.5, 5.5, 6.5) by banana homogenate and at different contact time (3 hours, 5 hours, and 7 hours). Afterward, the oxidized tea extract produced were to be examined its antioxidant activity along with the phenolic and flavonoid content. The result showed that pH of 4.5 for green tea extract in its reaction with banana homogenate gave higher phenolic content and flavonoid content compared to other pH. The optimum contact time was 3 hours, in which it gave higher phenolic and flavonoid content result for fermented tea extract produced. Longer contact time at 5 and 7 hours resulted in the decrease of both bioactive compounds. From LC-MS analysis, it was known that the amount of catechins compounds decreased after the reaction and followed with decrease in antioxidant activity. The loss of these catechins may be used as a marker to determine that this reaction was over-fermented.