Abstract: Objective: To investigate the synergistic antioxidant effects of different ratios of EGCG (epigallocatechin gallate) and isorhamnetin combinations, and provide a theoretical basis for the development of food borne flavonoid functional foods. Methods: The cellular antioxidant activities (CAA) of EGCG and isorhamnetiin combinations were estimated by Chou-Talalay combination Index (CI) method. Results: The median effective dose (EC₅₀) of EGCG and isorhamnetin combination (6:4, c/c) was 5.01±0.1 μg/mL with the CI_avg value of 0.76, which represented significantly synergistic effects. Further experiments proved that the superoxide dismutase (SOD) activities of EGCG+isorhamnetin (1.5+1, 3+2, and 6+4 μg/mL) were increased by 5.2%, 21.1% and 49.1%. Glutathione peroxidase (GSH-Px) activities were increased by 7.6%, 27.8% and 57.6%, and catalase (CAT) activities were increased by 5.6%, 24.6% and 42.1% of AAPH group value, respectively. Conclusion: The mechanism of the combination of EGCG and isorhamnetin in cell antioxidant activity might be through up-regulating the activity of endogenous antioxidant enzymes to enhance the cell's own antioxidant capacity, thereby achieving a balance in the body's oxidative stress response.