Transesterification of waste cooking oil with heterogeneous (heteropoly acid) catalyst and methanol has been investigated. Response Surface Methodology (RSM) and Artificial Neural Network (ANN) were employed to study the relationship between process variables and free fatty acid conversion and for predicting the optimal parameters. The highest conversion was 88.6% at optimum condition being 14 h, 65 degrees C, 70:1 and 10 wt% for reaction time, reaction temperature, methanol to oil molar ratio and catalyst loading, respectively. The RSM and ANN could accurately predict the experimental results, with R-2 = 0.9987 and R-2 = 0.985, respectively. Kinetics studies were investigated to describe the system. The reaction followed first-order kinetics with the calculated activation energy, Ea = 53.99 kJ/mol while the pre-exponential factor, A = 2.9 x 10(7) min(-1). These findings can help improve an environmentally friendly biodiesel process that conforms to ASTM D6751 standards. (c) 2012 Elsevier Ltd. All rights reserved.