Decreased antioxidant levels may be a cause of many diseases. Pus accumulation in the uterus literally called pyometra and generally occurs in median or late life span of bitches. The objective of the study was to evaluate the concentrations of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), oxidative stress parameter-thiobarbituric acid-reactive substances (TBARS) and inflammatory mediator, tumour necrosis factor alpha (TNF-α) in uterine tissues of bitches with and without pyometra. For this purpose, bitches with pyometra (n=27), and healthy bitches in dioestrus (n=8) included in the study and both of the groups went under ovariohysterectomy operation. SOD and CAT enzymes were found significantly higher in uterine tissues of dioestrus group (p<0.01, p<0.05, respectively). TNF-α did not differ in uterine tissues between the groups (p>0.05). Our data showing that decreased concentrations of antioxidant enzymes in the uterus occurs during the disease of pyometra in bitches. Due to antioxidants cannot deactivate free radicals occurred during the inflammatory process probably one of the main cause for uterine tissue damage in pyometra.