Distiller’s Dried Grains with Solubles (DDGS) derived from ethanol production with corn grains contained about 3 times more fat than the corn. The concentrated fat containing vitamin E and other components derived from the fermentation process is thought to possess an antioxidative function, although information about the antioxidative function of DDGS feeding to animals is limited, hence the effect of DDGS feeding of dairy cows on oxidative stress markers in plasma at high environmental temperatures was investigated. Six Holstein cows were divided into 2 groups, one of which was fed total mixed ration (TMR) including 20%DM of DDGS, while another control group was fed similar TMR without DDGS for 17 days at a high environmental temperature. The dry matter intake in the DDGS group was similar to the control group. In the DDGS group, the milk protein content was lower and the milk lactose content higher than those of the control group (P