Esterification of lauric acid with a new homogeneous acid catalyst, ammonium ferric sulphate (AFS), was used to get optimised reaction conditions in order to get the best methyl esters conversion by using the statistical modelling approach of response surface methodology (RSM). AFS acts as a new source of homogeneous acid catalyst and was optimised in this study to produce methyl ester. The Central Composite Design (CCD) and RSM were used to determine the relationship between reaction time, methanol to lauric acid molar ratio and catalyst loading to determine the optimum condition for the esterification process. This work reports the novel results of the optimum conditions obtained for esterification of lauric acid, which are 1.5 h of reaction time, 6:1 M ratio of methanol to lauric acid and 8 wt% loading of AFS catalyst to give the highest conversion rate of methyl esters at 99.8%. These reaction conditions were successfully applied and verified on the esterification of palm fatty acid distillate (PFAD) which demonstrated the ability of AFS to act as an acid catalyst in the esterification process with a conversion rate of 81.2% of methyl esters. Acid value of PFAD was also decreased from 185 to 41 mg KOH/g PFAD. (C) 2019 Elsevier Ltd. All rights reserved.