Abstract: In order to preliminarily explore the structure, immune and anti-aging activity of capsular polysaccharide (CPS) produced by Lactobacillus plantarum W1. In this study, CPS was extracted and prepared by enzymatic hydrolysis. The absolute molecular weight, functional groups and monosaccharide composition of CPS were analyzed by gel permeation chromatography system, Fourier transform infrared spectroscopy and high performance liquid chromatography. The immune and anti-aging activities of CPS were investigated using RAW264.7 cells and Caenorhabditis elegans (C. elegans) models. The results showed that CPS was a heteropolysaccharide with an average molecular weight of 5.49×10⁴ Da, consisting of glucose and galactose in a molar ratio of 3.12:1. Furthermore, CPS had been found to enhance the proliferation and phagocytosis of RAW264.7 cells, as well as promote the secretion of NO and cytokines, thereby exerting an immunomodulatory effect. At a concentration of 125 μg/mL, the secretion levels of TNF-α, IL-6 and IL-1β in RAW264.7 cells reached their maximum values, which were 1.26 times, 1.11 times and 1.96 times higher than those in the control group, respectively. Concurrently, CPS significantly enhanced the antioxidant system of C. elegans (P<0.05), prolonged their lifespan, and improved their stress tolerance. The average lifespan of nematodes under normal, oxidative stress and heat shock conditions reached its maximum at 125 μg/mL, with lifespan extension rates of 21.05%±0.21%, 42.86%±0.27% and 50.00%±0.27%, respectively. These findings indicate that CPS exhibits significant biological activity and has the potential to be utilized as functional excipients in food products.