A two-step method is proposed to obtain high selectivity and high conversion rate for producing additive triacetylglycerol of biofuel from its byproduct glycerol. The esterification of glycerol with acetic acid was carried out over resin and zeolites. Amberlyst-35 was found to be an excellent catalyst. The reaction conditions were optimized by testing catalysts. temperatures. feedstock ratios as well as loads of catalysts. The optimal conditions are temperature of 105 degrees C and an acetic acid to glycerol molar ratio of 9:1 with 0.5 g catalyst. After the 4 hour reaction of the optimal condition, the selectivity of triacetylglycerol reaches almost 100% in 15 min by adding thereto acid anhydride. Recycling experiments indicate that no significant deactivation of Amerlyst-35 occurred during the reaction. (C) 2009 Elsevier B.V. All rights reserved.