Abstract: In order to screen suitable strains for solid-state fermentation that can improve the nutritional components, phenolic content and antioxidant activity of quinoa, and provide a theoretical basis for the development of quinoa products, quinoa was treated by solid-state fermentation (SSF) with single and mixed microbial strains of Lactobacillus plantarum, Saccharomyces cerevisiae, Rhizopus oryzae, Aspergillus oryzae, and Neurospora sitophila were performed in quinoa for 30 and 48 h. Effects of SSF with different strains on the nutrients, phenolics content and antioxidant activity in quinoa were determined and analyzed. Results showed that: After SSF, the starch and insoluble dietary fiber content in quinoa decreased respectively from 54.61% to the lowest 39.32%, and 2.32% to the lowest 0.26%. While the soluble dietary fiber content increased from 2.58% to the highest 4.38%. With the extension of the fermentation time (from 30 to 48 h), contents of free polyphenols and flavonoids in quinoa increased by 1.72 and 1.72 times as much as those in unfermented quinoa respectively, and the contents of bound polyphenols and flavonoids increased by 2.88 and 1.84 times as much as those in unfermented quinoa respectively. Although the antioxidant activity and DPPH free radical scavenging ability of free phenols in quinoa decreased after fermentation, the total antioxidant activity, DPPH and ABTS⁺ free radical scavenging capacities of the bound phenols increased significantly (P<0.05). In general, the antioxidant activities of quinoa phenolics were significantly improved after SSF with mixed cultures for 48 h, especially for the fermented quinoa with three mixed strains of Lactobacillus plantarum, Saccharomyces cerevisiae and Neurospora sitophila for 48 h, which was the best combination of strains for SSF processing of quinoa.