Abstract: In order to explore the structural characteristics and immunomodulatory effects of pectic polysaccharides in Jasminum sambac flower waste, two polysaccharides, JSP-3 and JSP-4, were separated by water extraction, alcohol precipitation, deproteinization, anion exchange chromatography and gel chromatography. Its structural characteristics were analyzed with relative weight average molecular weight, monosaccharide composition, partial acid hydrolysis-LC-MS and NMR. Finally, the immunomodulatory effects of two polysaccharides were studied by using murine macrophage RAW 264.7 as a model, and measuring the effects on proliferation, phagocytosis, ROS production and secretion of NO, TNF-α and IL-6. The results showed that JSP-3 and JSP-4 were two homogeneous polysaccharides with relative molecular weights of 15.48 kDa and 44.75 kDa, respectively, mainly composed of galacturonic acid, rhamnose, galactose and arabinose, with different proportions of galacturonan domain (JSP-3: 32.87%±3.53%, JSP-4: 68.64%±0.67%) and rhamnogalacturonan domain (JSP-3: 61.12%±3.37%, JSP-4: 28.28%±0.46%), indicating that both are pectic polysaccharides. Compared with the control group, JSP-3 and JSP-4 have no cytotoxic effect within 12.5~100 μg/mL. At a certain concentration, it increased the production of ROS and the secretion of NO, TNF-α and IL-6, also promoted the phagocytosis of mouse macrophages significantly (P<0.05). At the same concentration, JSP-4 could stimulate cells to secrete more NO, TNF-α and IL-6 than JSP-3, indicating that JSP-4 had a stronger immunoregulatory effect, which might be associated with its higher proportion of galacturonan domain and relative molecular weight. The above research results preliminarily proved the immunomodulatory effect of pectic polysaccharide from Jasminum sambac flower waste, and would provide a basis for its potential application in immunomodulators.