Abstract: This study aimed to screen lactic acid bacteria (LAB) with high exopolysaccharide (EPS)-producing capacity from traditional yak yogurt in Western Sichuan, and to characterize the structure and functional properties of the EPS. Among 185 LAB strains isolated, Limosilactobacillus fermentum 197 was identified as a high EPS producer. The fermentation medium was optimized through single-factor experiments, and the EPS was purified using DEAE-52 and CL-6B column chromatography. The purified fraction EPS1 was structurally characterized by Fourier-transform infrared spectroscopy, gel permeation chromatography, and nuclear magnetic resonance, and its bioactivities were evaluated in vitro. The results showed that the optimal carbon and nitrogen sources for EPS production were maltose and soybean peptone, both at 40 g/L. After optimization, the EPS yield reached 1699.83±34.31 mg/L, representing a 5-fold increase compared to the original yield. The purified EPS1, with a yield of 15.07%, had a molecular weight of 2.11×10⁵ Da and was composed of rhamnose, arabinose, galactose, glucose, and mannose. It contained both α- and β-glycosidic bonds, exhibited a triple-helix structure, and displayed a flaky porous morphology under microscopy. In vitro assays demonstrated that EPS1 at 10 mg/mL exhibited scavenging rates against ABTS⁺, DPPH, and hydroxyl radicals of 57.07%, 46.54%, and 49.68%, respectively, and an α-amylase inhibition rate of 51.46%. This study reveals the relationship between the structure of EPS1 and its antioxidant and hypoglycemic activities, providing a theoretical basis for developing functional dairy products using LAB-derived EPS and offering new insights into the utilization of lactic acid bacteria resources from plateau pastoral areas.