The performances of Nb2O5-SiO2 catalysts prepared by sol-gel technique in the epoxidation of soybean oil with hydrogen peroxide have been investigated. The most active catalyst showed a good activity in epoxidation reaction but also a low selectivity to epoxide. The low selectivity has been attributed to the presence on the surface besides the Lewis acid sites, that promote the epoxidation, also of strong Bronsted acid sites, that promote the reaction of ring epoxide opening by hydrolysis. (c) 2012 Elsevier B.V. All rights reserved.