By the investigation and comparison of different interesterification reactions at fixed reaction time researchers usually selected 1 hour as a characteristic time for the synthesis stage of industrial biodiesel production. Investigation performed in this work shows that the equilibrium of interesterification reaction mixture of rapeseed oil with methyl acetate in molar ration of 1:18 in presence of potassium tert-butoxide in tert-butanol at molar ratio to oil 0.08 at 25 °C reach the equilibrium approximately after 50 min but at 55 °C after 10 min. The equilibrium compositions of the reaction mixtures at different temperatures are different. The concentrations of TG, FAME and TA during the interesterification reaction at 25 °C obey the pseudo-first order law which do not reflect the stoichiometry of this multiple elementary steps reaction.