To improve coagulation characteristics and to reduce dossage of chemicals in watertreatment, polyaluminium sulfate was manufactured by reaction of polymerization between aluminium sulfate and sodium aluminate. As the results of affirmation and performance test, the yield of product was about 24% from molecular cut off levels by ultrafilteration method. The type of molecular is nearly affirmated as a kind of complex like Alm. (OH)n^(3m-n)+ from Scanning Electr Electron Mipy(S.E.M.) and X-ray diffraction test. Since the synthesized polymer was supposed to be quasi, further study for stabilization was required.