The goal of the present study was to investigate the effect of cattle theileriosis on blood serum ascorbic acid and vitamin E levels as a 203 Assiut Vet. Med. J. Vol. 52 No. 108 January 2006 model for studying the blood oxidative status in parasitized cattle. A total number of 18 Holstein cows were subjected to the study. All animals were examined clinically and blood samples were collected for evaluation of blood parasite, hemogram picture and vitamin E and ascorbic acid levels. Out of the examined number, 8 cattle were found infested with ticks and showed clinical manifestation of blood parasite infection, which were confirmed by the positive blood film for Theileria infection. The rest of the animals were proved healthy and used as control group for the study. The results of the evaluation study of the chain-breaking antioxidants, vitamin E and Ascorbic acid, in the diseased group as compared to the control group revealed significant decrease in blood serum ascorbic acid (p < 0.01) and vitamin E (p < 0.01) levels. The hematological picture revealed significant decrease in total erythrocytes count, hemoglobin concentration and packed cell volume %. The over all results suggest the presence of an increased oxidative stress in Theileria-infected cattle which was manifested by the reduction of the chain-breaking antioxidants levels, ascorbic acid and vitamin E in the blood of parasitized animals. The results of the study recommend the supplementation of Theileria-infected cattle with sources of vitamin C and vitamin E in addition to traditional treatment to overcome the oxidative stress associating the infection and to avoid the possible complications of secondary vitamin deficiency.