A corrugated plates heat exchanger reactor showing very high productivity in the transesterification of soybean oil with methanol, in the presence of a homogeneous alkaline catalyst (KOH, sodium methoxide), has recently been tested. The reactor is a small size corrugated plates heat exchanger having a low distance between the plates of 1.5-2 mm. A surprising behavior has been observed according to which the conversion to biodiesel increases by increasing the overall flow rates. This can be explained by examining the fluid dynamic behavior of the system with a step test, at different flow rates, made on single-phase liquid fluid. The observed experimental data for the higher flow rates can roughly be approximated to a plug flow behavior despite the very low Reynolds numbers. This is due to the intervention of a very active micromixing. In this reactor the local turbulence favors the mixing of two immiscible liquid reactants approaching, in the case of biodiesel production, the chemical regime. In this work we have shown that by using corrugated plates heat exchanger reactors (CP-HEX reactors) of opportune geometry we can largely intensify the process of biodiesel production. The micromixing intensity in these reactors is very high, favoring the contact between immiscible reagents such as methanol and oil. Therefore, the reactor could generally also be used for other liquid-liquid reactions and more advantageously for very exothermic or endothermic reactions for the great efficiency of the plates exchangers in removing or supplying heat to the reaction interspace.