Sr-Al mixed oxides nanocomposite as Sr3Al2O6 was prepared by sol-gel method and used as a basic heterogeneous catalyst for transesterification of soybean oil to methyl esters (biodiesel) by methanol. The prepared catalyst was characterized using X-ray diffraction (XRD), Transmission electron microscope (TEM), thermogravimetric analysis (TGA/DTA), temperature-programmed desorption (TPD) and nitrogen adsorption-desorption techniques. The response surface methodology (RSM) based on the Box-Behnken design was employed to investigate the effects of methanol to oil molar ratio, reaction time, catalyst amount and specifically the effect of interaction between process variables on the conversion of oil to biodiesel. Results from this study revealed that individual as well as bilateral variables interactions significantly affect the yield of biodiesel. With this information, it was found that utilization of methanol to oil molar ratio of 25 and 1.3 wt.% of catalyst within reaction time of 61 min and gave the biodiesel yield of 95.7 +/- 0.5%. (C) 2013 Elsevier Ltd. All rights reserved.