Abstract: This study aimed to screen lactic acid bacteria (LAB) starters with high exopolysaccharide (EPS) production and to analyze their metabolic mechanisms. By assessing the EPS content in fermented skim milk co-cultured with nine laboratory-isolated EPS-producing LAB strains and commercial strains, the optimal starter (designated as the SW group) was identified as a composite of the laboratory-isolated Lactobacillus pentosus strain 15 and commercial strains. The EPS content and viscosity of skim milk fermented by the SW group were significantly (P<0.05) higher than those observed in the control group (S group). Through the integration of physicochemical analysis and LC-MS-based untargeted metabolomics, a total of 67 differential metabolites were identified, comprising 40 upregulated and 27 downregulated metabolites. Metabolic analysis indicated activation of the arginine biosynthesis pathway, as demonstrated by the upregulation of arginine and its precursor N-acetylglutamate-5-semialdehyde (NAGSA), alongside the downregulation of ornithine. Concurrently, the essential amino acid L-leucine was significantly upregulated. Organic acids, including 2-hydroxyhexanoic acid and hydrocinnamic acid, were found to modulate acidity, while the accumulation of benzoic acid contributed positively to shelf life extension. Furthermore, the upregulation of EPS synthesis precursors, specifically UDP-glucose and glucuronic acid, indicated that EPS synthesis predominantly involved glycosidic bond linkages among UDP-glucose, UDP-glucuronic acid, and GDP-mannose. Pathway enrichment analysis demonstrated that the cofactor biosynthesis pathway was the primary driver of the metabolic flux of EPS, with phenylalanine metabolism supplying essential nutrients and arginine biosynthesis facilitating the accumulation of functional components. Collectively, this study elucidated that the SW group enhanced nutritional value, antibacterial efficacy, and EPS production through multi-pathway metabolic regulation, thereby improving product texture and nutritional fortification. These findings offer a theoretical foundation for optimizing the quality of fermented foods.