Polyaluminum chloride (PAC), containing about 70% Al-b, with the Al concentration (0.35 mol/L) satisfying the in situ water treatment. was synthesized efficiently with a membrane reactor. The effects of the membrane molecular weight cut-off (MWCO), the membrane modules lengths and the reaction temperatures on the species distribution, pH values, pressure drops and flow rates of aluminum solutions were studied. It is found that lower membrane MWCO, shorter membrane module length and higher temperature are favorable for the synthesis of PAC with high Alb content. (C) 2004 Published by Elsevier B.V.