The methylprednisolone asetate (MPA) is an important and long acting member of synthetic glucocorticoids (GC). Although the suppressive effect of GC especially dexamethasone on nitric oxide (NO) synthesis is well known, the effect of MPA on NO production is not fully documented. This study evaluated changes in plasma NO levels before and on day 1, 4 and 7 after injection of two different therapeutic dose of methylprednisolone asetate (MPA; Depo-medrol) in healthy rabbits. The MPA was injected intramuscularly at 2.5 (Group I, n=6) and 5.0 (Group II, n=7) mg/kg doses. Blood samples were collected from auricular vein before and on day 1, 4 and 7 after injections and the NO levels were determined. MPA treatment decreased NO values on day 4 (P<0.001) in both groups. In conclusion, the role of therapeutic dose of long acting MPA administration on the decreased plasma NO levels should be considered by clinicians.