A field study with two summer maize cultivars ND108 and YD13 showed that increased field temperature (3 degrees C) at the stage from male tetrad to maturity had significant effects on their grain yield and quality. The grain yield of ND108 and YD13 decreased by 46.6% and 45.1%, grain crude protein content increased by 11.6% and 2.02%, ether extract content decreased by 38.9% and 9.6%, starch (mainly amylopection) content decreased by 7.0% and 8.4%, and lysine content decreased by 58.9% and 51.2%, respectively.