Abstract: A two-step biodiesel production from Waste Cooking Oil (WCO) has been optimized. Pre-treatment with ferric sulphate in acid catalysed esterification process preceded transesterification in order to reduce the free fatty acid level in WCO. The objective of this study was to investigate the relationship between reaction temperatures, reaction time and methanol to oil molar ratio in the pre-treatment step. Central Composite Design (CCD) and Response Surface Methodology (RSM) were utilized to determine the best operating condition for the pre-treatment step. The optimum pre-treatment conditions were 60°C, 3 h and 7:1 for reaction temperature, reaction time and methanol to oil molar ratio, respectively with a maximum Fatty Acid Methyl Ester (FAME) yield being 81.3%.