Markers of oxidative status may become important tools in conservation biology as a means of evaluating survival and reproductive expectations in organisms, as well as to elucidate the effects of anthropogenic impacts on populations living in their natural environments. The objective of the present study was to evaluate seasonal variations in oxidative status in a population of Tropidurus catalanensis through the analysis of lipid peroxidation levels and quantification of activity of the antioxidant enzymes superoxide dismutase, catalase, and glutathione S-transferase in liver, kidneys, and tail muscle. This lizard inhabits southern Brazil, in the Pampas grasslands. A total of 73 animals were collected over a 1-year period through active search and hand capture, separated into males and females, euthanized with ketamine hydrochloride, and frozen. A detailed approach on the variation of climatic variables over the seasons is also provided in order to subsidize a better comprehension of seasonal variation in oxidative stress biomarkers of T. catalanensis. Results obtained reveal that this lizard exhibits a clear pattern of seasonal variation in redox balance markers across different tissues. Antioxidant system of these animals is highly efficient, being able to maintain constant levels of lipid peroxidation in liver and muscle in males and in all tissues studied in females. In the renal tissue, an increase in lipid peroxidation was found only in males in spring. The enzymatic antioxidant defense system studied herein exhibited tissue and sex-specific responsiveness, and was possibly modulated by factors both abiotic (e.g., photoperiod, temperature, radiation, precipitation) and biotic (e.g., reproductive cycle, nutritional status, type of food consumed).