The ingredients to make biodiesel environmentally friendly are oil, alcohol, and catalysts to accelerate the reactions that occur, namely esterification and transesterification reactions. The heterogeneous catalyst calcium oxide as in previous research can be combined with Moringa stem powder with a 1:1 ratio so that biodiesel can be obtained. The purpose of this research is analysed the esters in biodiesel from used cooking oil and calcium oxide catalysts that are varied with and without Moringa stem powder based on weight ratio. The analytical methods used were proximate, bomb calorimeter, FTIR, and GC-MS. The results of the analysis of biodiesel from used cooking oil using moringa stem charcoal at a carbonisation temperature of 650°C and a holding time of 120 minutes with a size > 180 Mesh ≤ 100 Mesh, contained the most volatile compounds compared to the variation of calcium oxide and Moringa stem charcoal 1:1. This result is sup-ported by FTIR, the presence of ester-specific functional groups and GC-MS detected fatty acid ethyl esters including hexadecanoic acid ethyl ester, heptadecanoic acid ethyl ester, and other carboxylic acids. These compounds as volatile compounds were also detected to be the highest by proximate analysis and supported by their calorific value by bomb calorimeter.