Abstract: To study the antioxidant activity of polysaccharides from Dendrobium officinale, the polysaccharide was extracted and purified from Dendrobium officinale, and its preliminary structure was characterized. Free radical scavenging activity and inhibition of low density lipoprotein (LDL) in vitro oxidation of Dendrobium officinale polysaccharides were evaluated. The results showed that the total sugar content of the obtained Dendrobium officinale polysaccharide was 90.17%±3.90%, the protein content was 0.14%±0.05%, the ash content was 4.47%±1.42% and the glucuronic acid content was 2.53%±1.02%, the relative molecular weight was 23970 Da and the monosaccharides were mainly mannose and glucose in this test. Dendrobium officinale polysaccharide had certain free radical scavenging capacity. It could inhibit the production of conjugated diene in the oxidative modification system of LDL. The inhibition rate of thiobarbituric acid reactive substances (TBARS) by copper ion reached 57.46%±0.56% when the polysaccharide concentration was 3.00 mg·mL⁻¹. This study could provide theoretical support for the development of drugs for diseases such as arteriosclerosis due to LDL oxidation.