Chlorine disinfection is carried out for the purpose of sterilization of microbes existing in drinking water. Chlorination may cause the formation of disinfection by-products (DBPs) by the reaction of free chlorine with humic substance in the water. In particular, the DBPs including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), and haloketones exist in tap water. The US Environmental Protection Agency (US EPA) suggests 80 mug/L THMs and 60 mug/L HAAs as maximum contamination levels for drinking water. This study was performed to detect the level of DBPs in drinking water and to measure disinfection by-product formation potential (DBPFP) of raw water with four different properties. After 24 h of chlorination, the measured level of trihalomethane formation potential (THMFP), haloacetic acid formation potential, and haloacetonitrile formation potential ranged from 55.0 to 102.6 mug/L, from 9.1 to 23.6 mug/L, and from 10.3 to 33.6 mug/L, respectively. DBPFP was the highest at pH 7.0 and increased with the reaction time. Among the DBPFP, THMFP was detected more frequently than the others. In the treated water, DBPs were measured with a mean value of 47.0 mug/L. Chloroform, dichloroacetic acid, trichloroacetic acid, and dichloronitrile all known as hazardous compounds, were measured as major parts of DBPs.