Abstract: This study aimed to investigate the structural characteristics, bioactivity, and potential applications of Dendranthema morifolium polysaccharide. The polysaccharide was extracted using the water extraction and alcohol precipitation method. The phenol-sulfuric acid method and the Coomassie Brilliant Blue method were employed to determine the polysaccharide and protein contents, respectively. Spectroscopic and chromatographic techniques were utilized to characterize the structural features of D. morifolium polysaccharide. Additionally, its in vitro antioxidant and immunomodulatory activities were assessed through free radical scavenging assays and ELISA for immune factor secretion in RAW 264.7 cells. The results demonstrated that the total sugar and protein contents in D. morifolium polysaccharide were 96.72%±0.13% and 2.85%±0.34%, respectively. The polysaccharide consisted of arabinose, galactose, glucose, xylose, and mannose in a molar ratio of 0.052 2∶0.112 7∶0.799 9∶0.011 9∶0.023 2. The molecular weight and polydispersity index of D. morifolium polysaccharide were determined to be 45.253 kDa and 1.403, respectively. FT-IR and NMR spectral analyses revealed the presence of both β-glycosidic and α-glycosidic bonds, as well as a pyranose configuration. The in vitro antioxidant assays indicated that D. morifolium polysaccharide exhibited robust scavenging activity against DPPH and ABTS radicals at a concentration of 5 mg/mL, with scavenging rates of 75.48%±3.09% and 99.11%±2.19%, respectively. Furthermore, the scavenging efficiencies for superoxide anion and hydroxyl radicals were 47.88%±1.94% and 56.59%±1.37% at the same concentration. D. morifolium polysaccharide was found to be non-toxic to RAW 264.7 cells, and the levels of NO, TNF-α, IL-6, and IL-1β secreted by the cells were (91.29±6.62) μmol/L,((467.89±14.73) ng/L, (51.21±1.74) pg/L, and (61.63±30.70) ng/L, respectively, following treatment with 5 mg/mL of the polysaccharide. Collectivelly, these findings demonstrate that D. morifolium polysaccharide possesses significant antioxidant and immunomodulatory properties.