The increases in CO2 concentration and attendant temperature are likely to impact agricultural production. This study investigated the effects of elevated temperature alone and in combination with CO2 enrichment on grain yield and quality of soybean (Glycine max) and maize (Zea mays) grown in a Mollisol over five-year growing seasons. Plants were grown in open-top chambers with the ambient control, 2.1 °C increase in air temperature (eT) and eT together with 700 ppm atmospheric CO2 concentration (eTeCO2). While eTeCO2 but not eT increased the mean grain yield of soybean by 31%, eTeCO2 and eT increased the yield of maize similarly by around 25% compared to the ambient control. Furthermore, eT and eTeCO2 did not significantly affect grain protein of either species but consistently increased oil concentrations in grains of both species with eTeCO2 increasing more. The eT increased grain Fe concentration relative to the control treatment but decreased Ca concentration, while the relative concentrations of P, K, Mn and Zn varied with crop species. The elevated CO2 enlarged the eT effect on Fe concentration, but decreased the effect on Ca concentration. The results suggest that crop selection is important to maximize yield benefits and to maintain grain quality to cope with elevated CO2 and temperature of future climate change in this temperate region where the temperature is near or below the optimal temperature for crop production.