Mycotoxins contaminated feed is one of the most serious problems in poultry and animal production sectors. Therefore, the current study aimed to investigate the effects of dietary oregano essential oil (OEO) for 4 weeks against the adverse effect of aflatoxins (AFs) on immunity, oxidative stress, Total and differential leucocytes counts (TLC and DLC), interleukin 1 (IL-1), nitric oxide (NO), lysozyme enzyme activity, serum malondialdehyde (MDA), catalase, superoxide dismutase (SOD) and reduced glutathione (GSH). Beside growth performance [Weekly body weight gain and feed conversion ratio (FCR)] were also determined. A total of 132 male, 2 weeks old Japanese quails chicks (Coturnix japonica) were used in this study and equally divided into 4 groups. Group I is considered as negative control at which birds fed only basal diet, group II served as positive control and were fed AFs 2.5 mg /Kg supplemented basal diet, Groups III and IV were fed basal diet with 2.5 mg AFs /Kg and treated with OEO at a rate of 200 and 400 mg/Kg , respectively. Regarding growth performance, there was a significant (P<0.05)   reduction  in  weight gain and FCR at 4^th week of the experiment in group II, additionally different pattern was noticed in group IV which represented a significant (P<0.05) improvement as compared to the other AFs treated groups and was nearly similar to that of group I. Concerning Lipid peroxidation, oxidative stress enzyme and immune parameters at 4^th week of the experiment, MDA was significantly (P<0.05) increased in AFs treated quails (II and III) but  when AFs co-administered with 400 mg OEO, MDA was nearly similar to that of group I. The SOD, catalase, and GSH were decreased significantly (P<0.05) in groups (II and III) and was remarkably improved in group IV. The NO level was increased significantly (P<0.05) while lysozyme activity was decreased significantly (P<0.05) in group II, while they were decreased and increased in group IV, respectively. IL-1 and globulin as well as TLC were declined significantly (P<0.05) in groups II and III and improved nearly similar to control one in group IV. In conclusion, OEO has a potential and a protective effect against AFs B₁ immuno-deteriorating effect in Japanese quails especially at 400 mg/ kg dose.