Helically coiled tubes offer improved residence and thermal time distributions due to the formation of Dean vortices via centrifugal forces. Design and fabrication of several milli/microstructured helically coiled tube reactors are described for processes requiring a narrow residence time distribution (RTD) and efficient heat transfer at laminar flow regime. The performance of microstructured reactor capillaries, which provide a high specific surface area, is combined with a type of helically coiled tube, namely, a coiled flow inverter allowing for the narrowest RTD in laminar flow regimes. Axial dispersion is characterized by obtaining the RTD curves from different reactor setups. Overall heat transfer coefficients of a new reactor setup are measured in order to determine the heat transfer efficiency.