Abstract The transesterification of castor oil with maleic anhydride was studied using conventional and microwave heating. Reactions were followed by measuring the acid value and the reaction products were characterized by FTIR and 1 H NMR. A kinetic model that fit the experimental data was derived. The transesterification was non‐catalytic and first‐order with respect to each reactant. Non‐thermal effects of microwaves were not observed. Activation energy, enthalpy of activation, entropy of activation and free energy of activation were similar regardless of the heating method. Rate constants and the pre‐exponential factor were lower with the use of microwave heating, which could be a consequence of the decrease in the dielectric constant of the reaction liquid as the reaction progresses.