Effect of inhomogeneous mixing on chemical reactions in a Taylor vortex flow reactor was experimentally investigated by using a second-order reaction system. The flow-visualization experiment by a laser induced fluorescence method was also carried out to observe the cross-sectional view of mixing behavior in the inside of Taylor vortex cells. In the reaction experiment, the reaction among hydrogen peroxide, iodide ions and hydrogen ions, i.e. 2H(+) + 2I(-) + H2O2 --> I-2 + 2H(2)O, was used. The temporal evolution of the concentration of iodine was observed from the temporal variation of color of iodine. The flow-visualization experiment clearly revealed the existence of two different mixing zones within a Taylor vortex cell at low Reynolds numbers. Namely, the fluid flowing near the cell boundary was axially well-mixed, while the fluid element confined to the vortex core region was poorly exchanged with the outer well-mixed flow region. This vortex core region, called an isolated mixing region (IMR), decreased as increasing the Reynolds number. It has been found in the reaction experiment that the reaction rate is larger in laminar and singly-periodic wavy Taylor vortex flow regimes than in quasi-periodic and chaotic Taylor vortex flow regimes.