This study was conducted to evaluate the effect of dietary zeolite (clinoptilolite) supplementation on the oxidative/antioxidative status on plasma in healthy dairy cows. Twenty dairy cows were divided into two groups of 10. Control group was fed the basal ration for 60 days. Zeolite group was fed the basal ration supplemented with 2.5% zeolite daily. To evaluate the oxidative and antioxidative status comprehensively, indicators such as total oxidant status, oxidative stress index, total antioxidant status, lipid hydroperoxide, total free sulphhydryl groups, ceruloplasmin concentrations, arylesterase, paraoxonase-1 and catalase activities were measured in plasma. Lipid hydroperoxide concentration was significantly (P < 0.05) decreased from 6.21 +/- 0.94 to 4.90 +/- 1.05 mmol H2O2 Eq/l by zeolite supplementation. However, no significant effect was observed on the antioxidant and other oxidant indicators. In conclusion, although zeolite decreased the lipid hydroperoxide concentration, it cannot further strengthen antioxidant defense system in healthy dairy cows.