In this study, the catalyst ZnAl layered double hydroxides (LDH) were successfully being synthesised with molar ratios 4:1 and 3:1 via free-alkali method by using ammonia solution instead of sodium hydroxide. The catalyst has been characterised before and after calcination by using XRD, TGA, SEM, BET and FT-IR. Based on the XRD result, the crystalline peak was successfully obtained and collapsed into mixed oxides of zinc oxide after the calcination. The carbonate decomposition was analysed by TGA to confirm the decomposition temperature of carbonate anions which is 250 °C. The surface area performed by BET showing an increasing from 213 m2/g to 224 m2/g on ZnAl LDH. Carbonate anions were confirmed by FT-IR result which are at 1390 cm-1 and 856 cm-1. 1 wt% of calcined ZnAl LDH catalyst has been used in the transesterification reaction using waste cooking oil (WCO). The compositions of biodiesel that has been detected using GC-FID are laurate, myristate, palmitate, linoleate, and stearate.