Single-phase transesterification of palm oil with methanol catalyzed by homogeneous alkaline catalyst was carried out in a laboratory scale batch reactor at 298, 308 and 323 K in the presence of methylethylketone (MEK) as a co-solvent. Most of the previous research studies on single-phase transesterification by using a co-solvent were conducted to obtain higher reaction rates than two-phase. In the present study, the authors targeted to investigate the intrinsic reaction kinetics of transesterification of oil with methanol catalyzed by homogeneous alkaline. The reaction experiment was carried out at 0.1, 0.2 and 0.6 mol/L of palm oil initial concentration. The transesterification reaction rate constant behaved in a strange manner with the initial oil concentration: the rate constant increased with a decrease in the initial oil concentration. This may be attributed to size change of palm oil molecule with MEK concentration in palm oil-methanol-MEK system. © 2018 Elsevier Ltd.