Diseases caused by bacteria are still a serious health problem in the world. In many studies, oleic acid derivatives have bioactivity such as antibacterial activity. In this research, oleic acid was first esterified to form methyl oleate using methanol in the presence of sulphuric acid as the catalyst at 60°C for 4 hours. Further modification of methyl oleate structure was conducted by oxidation of C=C using a mixture of H2O2 and formic acid at 40 °C for 24 hours. The hydroxyl group from the oxidation reaction was converted into an ester by using gallic acid. Steglich esterification was employed and the molar ratio of diol and gallic acid was 1:2. The ester was characterized using FTIR and its antibacterial activity against Escherichia coli and Staphylococcus aureus was examined. FTIR spectrum showed the presence of ester and aromatic ring at 1750 cm-1 to 1600 cm-1. The antibacterial assay showed that the inhibitory zone of ester was 7 mm against E. coli and 6.8 mm against S. aureus which showed a slight improvement in antibacterial activity. © 2024 Author(s).