In this study, pre-chlorination and characteristic of algae`s coagulation by turbidities were investigated because of finding the best way to treat algae effectively. Coagulations for Microcystise aeruginosa were not affected by pre-chlorination. However, applied coagulants were increased to remove precursor of DBPs compared with those of coagulation without pre-chlorination. UV_(254) of treated water showed same results after applied coagulants were 3㎎-Al/L, so we could assume that treatment of organic matters were not affected by turidities of rawwater.