Objective To optimize the fermentation process of mixed lactic acid bacteria for grape leaves and to improve their antioxidant activity.Methods Using Lacticaseibacillus paracasei TM-27, Lactobacillus brevis KM-6, and Lactobacillus plantarum NG-120 as test strains, the optimal mixed strain ratio is selected by measuring pH, viable bacteria count, DPPH, ABTS⁺, and hydroxyl free radical scavenging rates, iron-reducing capacity, total polyphenol content, and total flavonoid content. Furthermore, key fermentation process parameters are optimized via single-factor experiments combined with response surface methodology.Results The optimal fermentation conditions of mixed lactic acid bacteria are as follows: the volume ratio of TM-27∶KM-6∶NG-120=1∶1∶2, fermentation time 69 h, fermentation temperature 43 ℃, and inoculation amount 4%. Under these conditions, the DPPH, ABTS⁺, and hydroxyl free radical scavenging rates are (76.43±0.74)%, (98.71±0.16)%, and (54.35±0.37)%, respectively. The iron reducing power is (65.65±0.28)%, the total flavonoid content is (1.728±0.002) mg/mL, and the total polyphenol content is (2.340±0.003) mg/mL. The measured values are in good agreement with the predicted values.Conclusion Mixed fermentation with lactic acid bacteria can significantly enhance the antioxidant activity of grape leaves.