The present study was conducted so that the possible effects of thermally-oxidised dietary oil and vitamin E supplementation could be determined on the performance, lipid peroxidation, antioxidant defence system and some blood and meat quality traits of broilers. Broilers were fed grower diets containing fresh or oxidised oil, supplemented with and without vitamin E (200 mg/kg) from four to six weeks of age. Neither oxidised dietary oil nor vitamin E supplementation had any adverse effect on weight gain, feed consumption or feed conversion ratio. However, the broilers that received oxidised oil had lower levels of plasma cholesterol and triglyceride compared to the control. The glucose level was neither influenced by oxidised oil nor by vitamin E supplementation. The plasma malondialdehyde level increased slightly in broilers fed oxidised oil, indicating increased lipid peroxidation. Higher glutathione peroxidise (GSH-P-x) activity observed in the broilers fed oxidised oil suggests greater oxidative stress. Vitamin E supplementation partly depressed GSH-P-x activity in broilers fed oxidised oil. This depression in enzyme activity might be the result of homeostatic compensation. The uric acid concentration was not affected by oxidised oil and vitamin E supplementation. Feeding oxidised oil did not cause a marked discolouration in breast meat. Vitamin E supplementation had some beneficial effects on colour measurements.