A lipase-immobilized dense sodium alginate membrane was prepared and used for the esterification of ethyl alcohol and lactic acid in a pervaporation reactor (PVR). From the solvent to the polymer, all materials were selected as natural and bio-based. The activity of the immobilized lipase was calculated from the batch reactor data in which the immobilized lipase was used as a heterogeneous catalyst. When the temperature was increased from 303 to 323 K, conversion was enhanced from 0.53 to 0.63 in PVR. The effect of the initial molar ratio on conversion was also investigated. As the molar ratio was increased from 1 to 3, conversion was enhanced from 0.53 to 0.62 in PVR. When the molar ratio continued to increase from 3 to 6, conversion decreased from 0.62 to 0.42. It was essential that the 80 % improvement in conversion had been achieved by using PVR compared to the batch reactor. It was also seen that the immobilized lipase used in PVR preserved its activity during the six experiments without a significant activity loss.