Background: Olive has a protective effect against chronic inflammatory conditions. However, it is not clear weather this effect is due to its immunomodulatory or antioxidant property. The aim of this study was to investigate the effect of olive leaf extract on serum levels of Th-17 related cytokines and its antioxidant properties. Materials and Methods: 40 male rats divided into 5 groups, and were treated by placebo (Control group), vitamin C (as a known and potent antioxidant) and different doses of olive leaf extract. Four test groups, received vitamin C 10 mg/kg and olive leaf extract which contained 5, 10 and 15 mg/kg Oleuropein. All treatments were applied for 10 consecutive days orally via gavage. After this period, cardiac puncture was performed to retrieve blood from animals in order to determine interleukin 17, 23 and TGF&beta; levels in their serum by ELISA method. Glutathione peroxidase (GPx), Superoxide dismutase (SOD), Catalase (CAT) activities and thiobarbituric acid reactive substances (TBARS, as a lipid peroxidation marker) were assayed in right brain hemisphere of treated animals. Results: TBARS increased significantly in control group when compared to the other groups (p<0.05). GPx and SOD enzymes indicated higher activity in the animal group which was treated with 15mg/kg Oleuropein, in comparison with control group and a group who treated with 5mg/kg Oleuropein (p<0.05). Although there were no significant difference in IL-23 and IL-17 levels among control and test groups (p>0.05), TGF&beta; concentration was significantly lower in animals which treated by 5 and 15 mg/kg of Oleuropein. Conclusion: Olive leaf extract, which contains Oleuropein, had a significant antioxidant effect on the brain of studied animals, while it was not able to change the Th-17 cell-related cytokines (Except TGF&beta;) significantly. Therefore, it could conclude that the protective role of olive against chronic degenerative diseases is related to its antioxidant properties rather than its effects on pathogenic cytokine profile of Th17 cells.