Objective To explore the role of Fas and FasL system in the pathogenesis of adult primary immune thrombocyto‐penic purpura (ITP) .Methods The peripheral anticoagulant venous blood samples were collected from the patients with newly di‐agnosed ITP and healthy adults .The expression rates of Fas and FasL in Th/Tc ,Th1/Th2 ,Tc1/Tc2 cells and their expression rates at platelet surface were detected by flow cytometry .Results The Fas and FasL expression rates on the surface of Th ,Th1 ,Th2 , Tc ,Tc1 and Tc2 in the ITP group were increased compared with the healthy control group(P<0 .05) .,meanwhile the FasL expres‐sion on the platelet surface was significantly increased (P<0 .05) ,but the expression of FasL on the platelet surface had no obvious change(P>0 .05) .Conclusion The Fas and FasL expression on T cell subsets and platelet surface in ITP patients is abnormal , which may be related with the pathogenesis of ITP .