Antioxidant enzyme activities of fish (Cyprinus carpio L.) were determined in order to detect the effects of pollution of the Sitnica River in Kosovo on fish physiology and biochemistry. Activities of three antioxi- dant defense enzymes as catalase (CAT), superoxide dismutase (SOD), and glutathione-S-transferase (GST) in the blood of fish were chosen as bioindicators. Fish (n=21) were sampled during March-May and August- September 2010-12 from Ferizaj, Vragoli, and Plemetin (Sitnica River). Plasmatic CAT, SOD, and GST were significantly higher (P<0.001) in fish from polluted Vragoli and Plementin sites than Ferizaj. Ferizaj is a source of the river site, so is less contaminated than the two other sites. These three enzymes constitute a sensitive biochemical bioindicator and can be used for detection of chemical pollution in fish. Based on results of our research we can conclude that the Sitnica River is polluted mainly by industrial and urban discharge of liquid waste products. As a consequence, legal actions need to be taken in order to prevent environmental pollution on the site.