Abstract: OBJECTIVE To investigate the clinical efficacy of Lienal Polypeptide Injection treatment of primary immune thrombocytopenia. METHODS 50 patients were randomly divided into the control group and the treatment group. the control group took oral corticosteroids, and the treatment group took oral corticosteroids combined with Lienal Polypeptide Injection. Then observed the effects of two groups and judgment standard for clinical effect. RESULTS The total effective rate was 84% in treatment group and 64% in control group. The blood platelets begin to rise had a rapid onset, time was shortened reaching peak and the effect last longer in treatment group. compared with before treatment, the platelet antibody, reticulated platelet, CD3⁺CD8⁺ of two groups were all decreased significantly(P<0.05), and thromocytogenic megakaryocyte, CD3⁺, CD3⁺CD4⁺ of two groups were all increased significantly after treatment (P<0.05). after treatment, there were remarkable differences between two groups in the index of platelet antibody, reticulated platelet and subset of T cells(P<0.05), while there was no significant differences between two groups in index of bone marrow megakaryocyte. No adverse reactions were observed in both groups. CONCLUSION The Lienal Polypeptide Injection has definite clinical effect in treating primary immune thrombocytopenia, and could be used in the clinical application.