Aim To extract and purify Cordyceps militaris polysaccharides (CMPS), analyze its molecular weight distribution and preliminarily explore its mechanism of cholesterol lowering. Methods CMPS was separated by hot water extraction and alcohol precipitation, and purified by sevage reagent and AB-8 macroporous adsorption resin. The molecular weight distribution of CMPS was determined by high-performance gel permeation chromatography. Then, the ability of CMPS to bind cholic acid salt was measured in a simulated gastrointestinal environment. Meanwhile, HepG2 cells were cultured and the effect of CMPS on proliferation rate and total cholesterol (TC) level was observed in HepG2 cells. The protein expressions of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA-R) and sterol regulatory element binding protein-2 (SREBP-2) in hepatocytes were analyzed by Western blot. Results The content of polysaccharides with molecular weight of 3 119 kDa in CMPS was the most, followed by 649 kDa and 20 kDa. The binding ability of CMPS to cholic acid salt was strong, and the binding rates of CMPS to sodium cholate, sodium taurocholate and sodium glycine cholate were respectively 63%, 62% and 50%. Cell culture showed CMPS concentration lower than 200 mg/L did not inhibit the growth of HepG2 cells after treatment for 24 hours. CMPS significantly down-regulated the protein expressions of HMG-CoA-R and SREBP-2 and decreased TC level in hepatocytes. Conclusion CMPS has the potential to lower cholesterol level.