The aim of the present study was to investigate the effect of dietary supplementation of organic selenium (oSe) on blood parameters of male broiler breeder under dexamethasone (Dexa) challange. Fifty broiler breeder roosters (Ross 308) at the age of 64 weeks were randomly allotted to five groups (10 roosters/group) and fed a standard diet supplemented with different levels of oSe during 10 successive weeks of the experimental period. To induce stress, dexamethasone (2 mg/kg body weight) was injected during weeks of 4 to 6 of the experiment, in one-day-interval manner. Experimental treatments including diet without oSe supplementation and Dexa treatments (negative control; NC), or treated with Dexa and different levels of oSe including 0 (positive control; PC), 0.15 (Se15+Dexa), 0.30 (Se30+Dexa) or 0.45 (Se45+Dexa) mg/kg of diet. During the experimental period, concentration of testosterone, corticosterone, malondialdehyde (MDA), total antioxidant capacity (TAC), hepatic enzymes activity (ALT and AST), uric acid, total protein, albumin, plasma lipid and glucose parameters, were evaluated every two weeks. Hepatic enzymes and glutathione peroxidase (GPX) activity, TAC, concentration of uric acid, total protein, albumin and glucose were not affected by the treatments (P<0.05). Dexamethasone injection increased plasma concentrations of total cholesterol, HDL, LDL and MDA in the PC group compared with the NC group (P<0.05). However, oSe ameliorated these negative impacts in dexamethasone-stressed roosters (P<0.05). Generally, the results of this study indicate that dietary inclusion of oSe improved the negative effects of Dexa on some blood parameters in roosters under dexamethasone challange.