This paper aims to formulate a model describing the overall transesterification rate of vegetable oil with methanol catalyzed by homogeneous catalyst. Transesterification of palm oil with methanol catalyzed by KOH was carried out in a laboratory scale batch reactor at 298, 308 and 323 K. The stirring speed of the reaction mixture was chosen at a level, at which methanol droplet external mass transfer may be negligible. The internal mass transfer was analyzed by applying the effectiveness factor concept developed for solid-fluid heterogeneous catalytic reaction system. The internal mass transfer was found to be negligible in this reaction system under the conditions applied in the present study. The authors reproduced the overall two-phase transesterification rate from homogeneous transesterification kinetic data and some required parameters by applying the model proposed in the present study. The factors which suppress the overall two-phase reaction rate are solubility of oil in methanol and methanol to oil volume ratio. © 2018 Elsevier Ltd.