This study was designed to investigate the immunoprotective effects of Radix Pseudostellariae fibrous root extraction(RPFRE) on immunosuppressed mice.KM male mice of 3~4 weeks old and weighing (20±2 g) were randomly divided into blank group (CK),cyclophosphamide (CY) model group,Astragalus polysaccharide group (APS),RPFRE low,medium and high dose groups,with 20 mice in each group.On the day of 1th-14th,mice both CK and CY group were given by distilled water,mice in ASP group were given by Astragalus polysaccharide at the dose of 200 mg/kg,RPFRE low,medium and high dose groups were administered by gavage in 100,200,400 mg/kg RPFRE;At the day of 15th-17th,mice in CK group were given by normal saline and the other mice were intraperitoneally injected with 80 mg/kg CY.On the 18th day,mice were weighed,blood sample was collected.The phagocytic function of macrophages was determined by carbon particle clearance test;the splenic lymphocyte proliferation ability was detected by MTT assay;the contents of cytokines (IL-2,IL-4,IL-6 and IFN-γ) in the serum were determined by enzyme-linked immunosorbent assay (ELISA).Contents of the serum immunoglobulin (IgG,IgM,IgA),complement (C₃ and C₄) were determined by immunoturbidimetry.The results showed as follows:compared with model group,the spleen index and liver index in high-dose RPFRE group were increased (P<0.01).The phagocytic index was increased (P<0.05),the SI of T and B lymphocytes were increased (P<0.01),IL-2,IL-4 and IFN-γ levels were increased (P<0.05) and the content of IgA,IgM and complement C₃ and C₄ were increased (P<0.01).It was concluded that RPFRE could antagonize the atrophy of spleen,thymus and liver caused by CY,and improve immune organ index;High concentration of RPFRE could interfere with the damage caused by CY,maintain the phagocytic ability of macrophages,promote proliferation of T lymphocytes,and antagonize the decrease of immunoglobulin and complement secretion induced by CY,thus exerting immunoprotection effects on immunosuppressed mice.