ABSTRACT The effects of oxidative stress induced by high temperature on the cell viability, proliferation, apoptosis and oxidative status of chicken embryonic fibroblasts (CEF) were analyzed. The viability, proliferation, apoptotic and anti-oxidative status were measured after incubating CEF at the temperatures of 37ºC (control) and 40-44ºC (experimental groups) for 6,12 and 24 hours. The results showed that at high temperature (42-43ºC), the viability of CEF cells decreased after 6, 12 and 24 h of incubation, but the difference was significant only at 43ºC. Cell proliferation was significantly reduced at 44oC/6h. The apoptotic rate of CEF cells was increased following heat treatments in a time-dependent manner. ROS formation increased with increasing temperature, but the difference was only significant at 44ºC/6,12h. Heat stress did not significantly affect the superoxide dismutase (SOD) activity. CAT activity was significantly decreased at 43ºC/24h and 44ºC/12 and 24h. Malondialdehyde (MDA) formation was significantly increased at 43ºC/12h and 44ºC/12 and 24h. In conclusion, heat stress induced the oxidative stress, decreasing the viability, proliferation and anti-oxidative response of CEF cells.