Canine transmissible venereal tumour (TVT) is a contagious cancer and sexually transmitted one dog to another by allogenic transfer of living cancer cells. The aim of this study is to examine the relationship between antioxidative metabolism and venereal tumour at Kangal Dogs and to show the size of oxidative damage it causes through 8-hydroxy-2'deoxyguanosine (8-OHdG). The materials of this study included the blood sera of 15 Kangal Dogs with TVT, and as a control group of 15 healthy Kangal Dogs. The sera levels of 8-OHdG were determined by competitive enzyme linked immunosorbent assay (ELISA) method. The level of malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) which are antioxidative enzymes were investigated by spectrophotometric methods as described. Serum 8-OHdG and MDA levels of dogs with TVT were found to be significantly increased compared to the control group (P<0.001). The levels of GPx were statistically different (P<0.05). In the light of the findings, which are obtained in this study, the transmissible venereal tumour, which is an infectious and treatable type of cancer, can lead to new studies that may be caused by oxidant-antioxidant metabolism.