Aim To observe the effect of cyclosporine A on serum interferon-γ(IFN-γ),nitric oxide synthase(NOS) and nitric oxide(NO) in patients with chronic aplastic anemia(CAA). Methods 60 CAA patients were randomly divided into two groups.Control group was given Yixuesheng,while observation group was given cyclosporine A on the basis of control group.Two groups serum IFN-γ,NOS and NO before and after treatment were compared. Results Control groups serum IFN-γ(27.4±3.3 ng/L),NOS(30.8±4.0 kU/L) and NO(28.1±2.7 μmol/L)after treatment had no obvious change.Observation groups indexes(21.7±2.5 ng/L,22.3±3.6 kU/L和9.5±1.8 μmol/L)were obviously lower than before treatment and control group(P<0.05). Conclusion Cyclosporine A can decrease serum NO through inhibition of bone marrow failure,and thus reduce the damage degree of oxygen free radical and protect vascular wall in a certain degree.