To investigate the role of IL-18 and IL-18BP balance in aplastic anemia (AA).A total of 29 AA patients and 22 controls were recruited in present research. The expressions of IL-18 and IL-18BP were measured by enzyme-linked immunosorbent assay (ELISA). The mRNA expressions of IL-18 and IL-18BP were measured in all subjects using real-time quantitative polymerase chain reaction (RT-PCR).The levels of the IL-18 in plasma of AA and normals were (365.5 ± 160.6) pg/ml and (175.9 ± 92.8) pg/ml (P < 0.01); and the expression of IL-18 in severe AA patients (441.3 ± 116.9) pg/ml were higher than that in non-severe AA patients (326.4 ± 167.0) pg/ml (P < 0.05). The level of IL-18BP was increased in plasma of AA (1788.6 ± 523.8) pg/ml than in normals (1083.6 ± 489.6) pg/ml (P < 0.05). But the ratio of IL-18/IL-18BP in AA patients was much higher than that in controls (P < 0.05). RT-PCR revealed the levels of IL-18 and IL-18BP mRNA were up-regulated in AA patients when compared to controls, but the ratio of IL-18/IL-18BP was significantly elevated in AA patients.IL-18/IL-18BP imbalance may play an important role in pathogenesis of AA and regulating the balance of IL-18 and IL-18BP may be a therapeutic approach to AA.