Abstract： Objective To investigate the expression of serum thrombopoietin (TPO) in patients with hemophagocytic syndrome (HPS) and to evaluate its clinical significance. Methods The clinical data of HPS patients from Beijing Friendship Hospital,Capital Medical University during the period from September 2008 to July 2010 were collected. They were divided into infection-associated HPS,tumor-associated HPS and rheumatological disease associated HPS according to different causes. The serum concentration of TPO in HPS patients and 26 healthy controls was measured with enzyme-linked immunosorbent assay (ELISA). Then the correlations between TPO and laboratory indicators was analyzed. Results The level of serum TPO in 26 cases of HPS was significantly lower than that of control group (P =0.001) and the variance was not statistically significant in different causes of HPS groups using ANOVA (P =0.183). The TPO levels in HPS patients showed positive correlations with serum creatinine,after we detected their TPO levels and platelets,red blood cells,hemoglobin,serum creatinine,urea nitrogen,triglyceride,fibrinogen,ferritin,NK cell activity and sCD25 levels on the same day. Conclusion TPO together with various cytokines may affect the formation of blood cells in HPS patients,and its reduction may be associated with impaired liver function. The underlying mechanism remains to be further explored.