Zinc aluminate is a material with high thermal stability and high mechanical strength that, owing to these properties, is used as a catalyst or support. In this work, zinc aluminate spinel was synthesized by the microwave hydrothermal method in only 15 or 30 min at a low temperature (150 degrees C) without templates, using only Al(NO3)(3)center dot 9H(2)O, Zn(NO3)(2)center dot 6H(2)O, and urea as precursors and applied in the transesterification of soybean oil. X-ray diffraction analysis showed that ZnAl2O4 had a cubic structure without secondary phases. The nitrogen adsorption measurements (BET) revealed a high surface area (266.57 m(2) g(-1)) for the nanopowder synthesized in 15 min. This powder showed activity of 52.22% for the catalytic conversion of soybean oil into biodiesel by transesterification. (C) 2015 Elsevier Ltd. All rights reserved.