This research studied the effect of factors that are able to form disinfection by-products (DBPs) of chlorination, including natural organic matter (NOM) with sewage, bromide ions, pH and contact time. Trihalomethane (THMs) yield of $0.95{mu}mol/mg$ was higher than other DBPs yield for the chlorinated humic acid samples. THMs yield of sewage sample was $0.14{mu}mol/mg$ and haloacetonitriles (HANs) yield in the sewage samples were $0.13{mu}mol/mg$ but only $0.02{mu}mol/mg$ for the humic acid samples. As the concentration of bromide ions increased, brominated DBPs increased while chlorinated DBPs decreased, because bromide ions produce brominated DBPs. THMs were highest $(55.55{mu}g/L)$ at a pH of 7.9 and haloacetic acids (HAAs) were highest $(34.98{mu}g/L)$ at a pH of 5. Also THMs increased with increasing pH while HAAs decreased with increasing pH. After chlorination, the rate of THMs and HAA formation are faster at initial contact time and then reaches a nearly constant value after 24 hours. This study considers ways to reduce DBP formation by chlorination.