The catalytic activity of a phosphazenium hydroxide (PzOH) catalyst incorporated onto silica (PzOH/SiO2) was investigated in the transesterification of vegetable oils with methanol. The PzOH stably incorporated onto silica (SiO2) maintained its basicity and converted methanol molecules to methoxide ions. The PzOH/SiO2 catalyst exhibited high activity in the transesterification of palm, corn, grape seed, and soybean oils (S-oil) with methanol, achieving similar to 90% conversion at 75 degrees C with a catalyst loading of 0.2 g per 4.8 ml of S-oil. Although the accumulation of organic materials on PzOH/SiO2 reduced its activity, this accumulation was effectively removed by washing with methanol. The high activity of PzOH/SiO2 was responsible for its strong basicity and for the free mobility of the PzOH moiety. (C) 2010 Elsevier B.V. All rights reserved.