Abstract: In this research, the focus was on investigating the release and enrichment of polyphenols in quinoa subsequent to fermentation by a blend of Lactobacillus. The study employed a composite fermentation approach using three distinct strains of bacteria, with the inoculation amount, fermentation time, and water addition as the primary variables. Both univariate and response surface methodologies were utilized to refine the quinoa fermentation technique. The study also compared and evaluated the variations in polyphenol levels, antioxidant properties, and bioavailability following in vitro simulated digestion, both prior to and post-fermentation. The results showed that the most effective conditions for the fermentation of quinoa by a blend of Lactobacillus involved an inoculation rate of 13%, a duration of 38 h for the fermentation process, and a moisture level of 51%. With these refined parameters, the content of polyphenols achieved 6.94±0.09 mg GAE/g, which was 2.83-fold greater than that in the non-fermented group. After fermentation, the antioxidant activity of quinoa polyphenols increased. Following a simulated in vitro digestion, compared to the unfermented group, the polyphenol content in the fermented group increased significantly by 3.3 times, and its bioavailability increased by 17.44%, and a marked improvement in the DPPH and ABTS⁺ radicals scavenging rates (P<0.05). Overall, the fermentation of quinoa by a combination of Lactobacillus facilitates the accumulation of polyphenols and augments its antioxidant capacity, offering insights for the innovation of quinoa-based functional foods.