Experiments were conducted in electroosmotic flow (EOF) with 0.005≤Re ≤ 0.039 on mixing enhancement in 3-D helical microchannels. Both inlet velocity and concentration distribution along the flow channel were measurement via £gPIV and £gLIF technique respectively. The experimental results showed that the helical channels can generate nearly fully chaotic flow and achieve the complete mixing in a relatively short channel with three different helical channels (3, 4, and 6 inlet channels), and the four-inlet channel found to have the best mixing efficiency. Finally, the mixing length was correlated into a form of £f/Dh = 2.8Pe0.35 within ¡Ó8% accuracy between the experiments and prediction.