Aquatic ecosystems are becoming increasingly inundated by noxious chemicals, such as pesticides, through human activities. These chemicals combined with other stressors like heat stress create volatile environments that negatively affect the physiological functions of aquatic organisms. Through this research, we observed the dose-dependent effects of pesticide cocktail (metalachlor, linuron, isoproturon, tebucanazole, aclonifen, atrazine, pendimethalin, azinphos-methyl for 1-month exposure) combined with elevated temperatures (32°C for 1-month exposure) on morphology of gills and kidneys, and expression of catalase (CAT, an antioxidant), superoxidase dismutase (SOD, an antioxidant), and renin in kidney tissues of goldfish (Carasius auratus, a model teleost species). Histopathological analysis showed wide-spread damage to both gill and kidney tissues in higher temperature and pesticide co-exposure groups, including extensive fusion of secondary lamellae, club-shaped primary lamellae, rupture of epithelial layer, loss of normal architecture, glomerular shrinkage, hemorrhaging, and degeneration of tubular epithelium. Immunohistochemical analysis demonstrated a change in CAT and SOD expressions in kidney tissues in combined exposure to pesticide and higher temperature compared to control (22°C). Expression of renin in kidney tissues was also altered with varying doses of pesticides and elevated temperature. Collectively, our results suggest that the combined effects of heat stress and pesticides cause cellular damages, as well as down-regulate the osmoregulatory and antioxidant enzyme activities in gill and kidney tissues of common goldfish.