Abstract: In this study, a homogeneous polysaccharide fraction was extracted and purified from the rhizome of Polygonatum sibiricum, its physicochemical properties and protective effect against oxidative damage were analyzed, and its potential protective mechanism was initially explored. The homogeneous polysaccharide (PSP) was obtained by water extraction, alcohol precipitation, and separation on DEAE-52 cellulose and Sephadex G-100 columns. The phenol sulfate method, m-hydroxybiphenyl method, high performance gel permeation chromatography and Fourier infrared spectroscopy were used to analyze the physicochemical properties of PSP. The in vivo antioxidant effects of PSP were investigated in a mouse model of D-galactose induced oxidative damage. The results showed that the carbohydrate content of PSP was 94.42%±14.73% and its molecular weight was 5566.41 Da. PSP was also found to contain β-type furan or pyran fructose, as well as longer branched chains with more branches. Compared with the model group, the levels of SOD, GSH-Px and T-AOC significantly increased (P<0.05), and MDA levels significantly decreased (P<0.05) in serum, brain tissue and liver tissue of the PSP high dose groups, HE staining revealed that liver damage was significantly ameliorated and the expression of Nrf2 and HO-1 protein in the liver was significantly enhanced in the PSP-treated group (P<0.05). It could be concluded that PSP had a protective effect on oxidative damage in mice, and its protective mechanism might be related to the Nrf2/HO-1 signaling pathway.