The ability of bis(acetyl-acetonato)dioxo-molybdenum (VI) [MoO2(acac)(2)] to catalyse the epoxidation of soybean oil in the presence of tert-butyl hydroperoxide as oxidizing agent has been investigated. The influence of reaction time and temperature in the course of the epoxiclation reaction was evaluated by quantitative H-1 NMR. When epoxidation was carried out in refluxing toluene at 110 degrees C for 2 h. a 70.1% conversion of substrate was obtained, producing 54.1% epoxidation with a selectivity of 77.2%. The H-1 NMR spectroscopic method selected for the purpose of this work allowed a simple and rapid evaluation of the mono- and diepoxides obtained following the epoxidation of soybean oil. (C) 2010 Elsevier B.V. All rights reserved.