In this present work, biodiesel production from grease trap waste (GTW), which was supplied by an environmental service company in Adelaide, was carried out employing sulphuric acid and potassium carbonate as catalysts for esterification and transesterification process respectively. The main variables involved in the synthesis of biodiesel, including alcohol types, alcohol/grease trap ratio, amount of catalyst, reaction time, and reaction temperature, were analysed. The complicated two-step process including esterification and transesterification has been applied due to the higher level of free fatty acid in the feedstock. The obtained results showed that average biodiesel yield produced decreased in the following order: isopropanol>propanol>ethanol>butanol. The optimum experimental conditions, which were obtained from the esterification process, were ethanol/oleic acid ratio 3:1, with 5 vol% sulphuric acid catalyst, reaction time 120 minutes, and reaction temperature 65oC. The conversion obtained at the optimum condition is 95.9%.