Abstract: Objective: To investigate the expression and clinical significance of serum interleukin-18(IL-18) and IL-18 binding protein (IL-18BP) in aplastic anemia (AA)patients.Method: Serum IL-18 and IL-18BP levels of 25 cases of AA patients and 25 healthy people were detected by ELISA,and IL-18 and IL-18BP mRNA expression was detected by real-time quantitative RT-PCR.Result: Compared with the normal control group (178.6±100.2) pg/ml,serum IL-18 levels of AA was(363.5±150.5) pg/ml,which was significantly higher (P<0.01).The level of IL-18 in patients with severe AA (442.5±124.1) pg/ml was obviously higher than that of chronic AA patients (319.2±158.3) pg/ml. serum IL-18BP of AA(1694.2±516.3) pg/ml was significantly higher than that of normal control group (1082.6±468.7) pg/ml (P<0.05).IL-18/IL-18BP ratio was significantly higher in AA patients. RT-PCR results confirmed that IL-18 and IL-18BP of AA patients were significantly increased when comparing with the normal control group,and IL-18/IL-18BP ratio increased.Conclusion: IL-18 and IL-18BP might have a close relation to the occurrence and development of AA as well as its immune mechanisms.IL-18/IL-18BP balance might be of important significance for clinical diagnosis and treatment.