The transesterification of soybean oil with methanol to fatty acid methyl ester (FAME) was carried out using WO3/SnO2 solid as a heterogeneous acid catalyst. The effects of catalyst preparation parameters on the conversion to FAME were investigated. This WO3/SnO2 catalyst prepared by an impregnation method, with the WO3 loading amount of 30% and calcined at a temperature of 1173 K, showed the best catalytic activity. The maximum conversion to FAME of 79.2% was achieved after 5 h at 383 K when 30:1 M ratio of methanol to oil and 5 wt.% of catalyst were employed. The ability of the catalyst to esterify free fatty acids (FFAs) in feedstocks and its insensitivity to water exhibited the potential to prepare biodiesel from low-cost feedstocks. The solid catalyst can be reused for four runs without significant deactivation. (C) 2012 Elsevier B.V. All rights reserved.