The potent ameliorating effect of ethanol extract of N. sativa seed on the immune system has been assessed in dexamethasone-induced immune-suppressed male rabbits. Fifty mature male rabbits were randomly assigned into five equal groups (control and four treated groups). Animals were daily treated, for 42 days, as follow: C: was orally administered with drinking water; T1: was orally administered with N.s.S.E. (1.5 g/ kg, b.w.); T2: was injected with dexamethasone (2 mg/ kg, b.w., im); T3: was combined treated concomitantly with N.s.S.E. and dexamethasone; T4: was treated with dexamethasone for 21 days followed by N.s.S.E. for 21 days. The results of body weight gain revealed significant increase in T1 and significant decrease in T2 among the experimental groups. Submandibular lymph node weights of T1, T2 and T3 were significantly higher than that of C. Kidneys weights in T2 and T3 registered significant increase compared with C. Bone weight in T1 and T4 groups was significantly higher than that of other groups. Liver weight in T2 was significantly higher and in T4 was significantly lower than other groups. Total leucocytes count and lymphocytes, monocytes and eosinophils percentages were significantly decreased in T1, while showed no significant differences in T2, T3 and T4 groups compared with that of control. Phagocytes activity and bone marrow mitotic index were significantly reduced in T2 group, while returned to normal in T1, T3 and T4 groups compared with control. Titers of IgM, IgA, C3, and C4 showed no significant differences among groups, while IgG titer was increased in T1 and T4 and decreased in T2. On the basis of the results obtained, it can be concluded that the examined extract showed a certain immunomodulating effect. Of the immunological aspects, cellular immunity was potentially ameliorated in intact and dexamethasone-induced immunosuppressed- male rabbits.