[Objective] To analyze the components and structure of Opuntia milpa alta polysaccharides, and to study its anticoagulant activity. [Method] The crude polysaccharides （CP） were prepared from Opuntia milpa alta using hot water extraction and ethanol precipitation method, purified by anion-exchange chromatography and gel filtration chromatography to study its monosaccharide composition, weight-average molecular weight distribution and main chain structure. And a preliminary study was conducted on the anticoagulant activity of polysaccharide components. [Result] The polysaccharide components WSP1, WSP2a and WSP3 were obtained from CP by the anion-exchange chromatography and gel filtration chromatography. WSP1 was mainly composed of galactose with a weight-average molecular weight of 2.32×106. WSP2a consisted of rhamnose, arabinose, xylose, mannose, glucose, galactose, glucuronic acid and galacturonic acid, the contents were 6.3%, 32.3%, 12.9%, 1.5%, 4.8%, 37.1%, 0.64% and 4.4%, respectively. WSP3 mainly composed of arabinose, xylose, rhamnose and trace of glucose, mannose, uronic acid. The weight-average molecular weight of WSP2a and WSP3 was 1.24×106 and 7.92×106, respectively. WSP2 prolonged the activated partial thromboplatin time （APTT） and thrombin time （TT）, while had no significant effect on the prothrombin time （PT） in vitro, indicating that anticoagulant activity of WSP2 functions by affecting the intrinsic coagulation system. The test of inhibition to the conversion of fibrinogen into thrombin showed that WSP2a and WSP3 had obvious anticoagulant activity. Methylation analysis indicated that the main chain of WSP2a was constituted of 1, 4-GalA, 1, 2-Rha and 1, 2, 4-Rha. [Conclusion] This study provided experimental basis for the optimization and development of polysaccharide resources from cactus
