Surface tension is important due to its affect on fuel spray and atomization processes. Fuel drops tend to breakup easier at smaller surface tension, which leads to smaller Sauter Mean Diameter of the spray and enhanced evaporation. Despite its importance, there are few data on the surface tension of alcohol + diesel fuels and even less are available on its temperature and concentration dependence. To overcome this limitation, this work reports experimental surface tensions of ethanol, n-butanol and diesel at different temperatures, and the experimental surface tensions of ethanol/n-butanol + diesel mixtures at 7 mass fractions at different temperatures. The experimental data showed that mixture surface tension decreased linearly as temperature increased and it also decreased monotonically while alcohol mass fraction increased. The results were correlated with concentration and temperature using the least square fitting method. Finally, by analyzing the experimental conclusions, the Surface Tension Mixing Function was proposed to describe quantitatively the effect of concentration on binary fuel mixtures surface tension.