For many reactive processes, fluid mixing has a significant effect on the rate of a chemical reaction and on the quality of the product. Mixing in a chaotic flow reactor is a promising phenomenon to control and optimize chemical processes. The effect three-dimensional (3-D) chaotic flow advection on mixing efficiency and on chemical reaction advancement is examined. An experimental comparison is made, for low Reynolds numberflows, between two tubular reactors made of successive bends, with the same number of bends (equal to 80) mounted in different configurations : a helical configuration (for regular flow) and a chaotic flow configuration with bends in perpendicular planes. We show that the mixing and the chemical reaction (for an instantaneous bimolecular chemical reaction) are more efficient in the chaotic flow reactor than in the helical reactor. The different effects of chaotic advection, molecular diffusion and reaction are discussed in view of laboratory findings. (c) 2005 American Institute of Chemical Engineers