Abstract: The evolution of antioxidant activity during wort fermentation and the effects of fermentation process parameters including the wort gravity, yeast inoculation amount, yeast generation and fermentation temperature on the antioxidant activity of green beer were studied systemically in order to improve the antioxidant activity and flavor stability of beer. Results showed that wort fermentation resulted in significant increases of 6. 27%, 3. 46% and 31. 38% in DPPH radical scavenging activity, oxygen radical absorbance capacity and reducing power for green beer, respectively. The increase of wort gravity (from 6 to 12°P) led to significant increases in DPPH radical scavenging activity, oxygen radical absorbance capacity and reducing power of green beer, whereas slow growth or slight decrease in antioxidant indices was detected when the wort gravity exceeded 12°P. In the range of 8 to 32 million/mL, the higher yeast inoculation amount resulted in the higher antioxidant activity of green beer. From 1 up to 5 generation, the antioxidant activity of green beer declined as the yeast generation increased. Furthermore, the antioxidant activity of three green beers (fermented at 9, 12 and 15℃, respectively) decreased with the rise of fermentation temperature. Thus, it might be one of effective measures to improve antioxidant activity of beer by optimizing the fermentation process parameters.