This paper presents a study of the epoxidation of vegetable oil in an isothermal batch reactor system equipped with microwave or conventional heating. The epoxidation reaction was performed by peroxycarboxylic acid formed in situ from carboxylic acid and hydrogen peroxide. It was demonstrated that microwave irradiation can accelerate the epoxidation velocity when the continuous phase is aqueous, which is not transparent to microwave. This tendency was observed for peroxyacetic and peroxypropionic acids. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.