Objective:To study the effects of the polysaccharide from the pseudobulbs of Oreorchis patens on immunocompromised mice. Methods Immunocompromised mice was made by intraperitoneal injection of cyclophosphamide. The mice were divided into control group, model group, positive group, and high-dose, medium-dose, low-dose Oreorchis polysaccharide groups(270 μg/g, 135 μg/g, 67.5 μg/g) and were respectively treated with the according methods. Then the spleen index, thymus index, delayed-type hypersensitivity(DTH), serum hemolysin and phagocytic coefficient were measured.  Results: There were striking differences in the immunologic indexes between the control group and model group(P<0.05). Compared with the model group, the spleen indexes increased in positive group, and high-dose, medium-dose, low-dose Oreorchis polysaccharide groups; medium-dose Oreorchis polysaccharide group had some effects on delayed-type hypersensitivity(P<0.01); high-dose Oreorchis polysaccharide group had some impacts on all immunologic indexes(P<0.01).  Conclusion: High-dose Oreorchis polysaccharide can boost immunity in immunocompromised mice.