Abstract: To investigate the immunomodulatory and anti-aging activities of capsular polysaccharides (CPS) from Lactobacillus fermentum S1, this study first determined the effects of CPS concentration on the viability, phagocytic activity, acid phosphatase activity, NO production, and cytokine secretion levels in RAW264.7 cells, and evaluated its immunomodulatory activity. Subsequently, using Caenorhabditis elegans as a model, the effects of CPS on C. elegans lifespan, oxidative/heat stress resistance, and reproductive capacity were assessed to explore its anti-aging properties. The results indicated that within the range of 25~200 μg/mL, CPS significantly enhanced cell proliferation ability, phagocytosis rate, and acid phosphatase activity in RAW264.7 cells, and promoted the release of NO and cytokines IL-6, IL-1β, and TNF-α by up-regulating the expression of related genes (P<0.05). Compared to control group, the maximum increase in cell viability, phagocytosis rate, and acid phosphatase activity in the CPS-treated group reached 58.22%, 33.48%, and 39.5%, respectively. The maximum secretion levels of NO, IL-6, IL-1β, and TNF-α increased by 101.29%, 31.33%, 161.08%, and 79.90%, respectively, demonstrating good immunomodulatory activity. The C. elegans experiment showed that treatment with 50 μg/mL CPS extended lifespan of C. elegans under normal, oxygen-stressed, and heat-stressed conditions by 19.87%, 39.39%, and 29.02%, respectively, suggesting strong anti-aging activity. CPS also effectively improved the RT-qPCR analysis revealed that CPS exerted its anti-aging effect through co-regulation of insulin signaling pathway (Daf-16 and Sir-2.1) and heat shock signaling pathway (Hsf-l and Hsp-16.2) in C. elegans. These findings indicate that CPS possesses good immunomodulatory and anti-aging activities. This study provides theoretical support for the application of CPS produced by lactic acid bacteria in immunoregulation and anti-aging products.