Chlorine which is nowadays the most commonly used disinfectant, interacts aquatic organic matter and causes formation of harmful disinfection by products. For this reason, number of researches on chlorine dioxide as a disinfectant alternative to chlorine, increased in recent years. After disinfection via the chlorine dioxide, chlorite and chlorate which defines as inorganic by products are formed. Chlorite total maximum concentration in water is limited as 1 mg/L as by USEPA. WHO limits total maximum chlorite concentration as 0.7 mg/L in water. There is no detailed study has been conducted for determination of the limit value yet in our country. In this study; after 0.25; 0.50; 0.75; 1; 1.25 and 1.5 mg/L chlorine dioxide had been dosed to Omerli raw water samples taken in December, and February; disinfection by products: chlorite, chlorate, THMs, HAAs and water quality parameters such as TOC, chloride, floride, bromide, sulphate and nitrate were analyzed and effect of the pH and contact time also investigated.