The characteristic floc growth of Al-based coagulants was investigated in the aspect of mixing intensityand visualization of generated flocs during coagulation and flocculation processes. Zeta potential of turbid particles inthe artificial water nearly approached to zero at pH 8-9, in which TDS and conductivity were minimized. The removalrate of turbidity and phosphate was maximized at the optimal mixing intensity of rapid and slow mixing stages. After therapid mixing stage of coagulation process, small particles (3-5μm) were abruptly generated, and higher mixing inten-sity made more numbers of flocs. With the progress of slow mixing stage, the number of small particles were decreasedwith the simultaneous increase of intermediate particles (7-21μm). The number of large particles (>23μm) were max-imized at the lowest rapid mixing intensity of 95.1 sec-1, whereas small particles (<5μm) were maximized at the highestrapid mixing intensity of 760.7 sec-1.