Formation of disinfection by-products (DBPs) from chlorination of Escherichia coli, a bacterial strain which was commonly found in drinking water as a representative of aquatic microorganism, was investigated under selected conditions. Evaluated factors included contact time, chlorine dosages, pH and bacterial concentrations. These factors potentially influence the DBPs formation in the disinfection systems, which could be optimized for minimization of DBPs formation during chlorination of drinking water. Results showed that the formation of DCAN from the bacterial suspension initially increased and then decreased with increased chlorine dose. The formation of 1,1,1-TCP and DCAN followed a similar pattern of increase and then decrease with prolonged reaction time. At the same time, the concentrations of DCAA, TCAA, TCNM and 1,1,1-DCP decreased when pH was increased from 5 to 9. Bacterial contamination in aquatic environments has been extensively reported in recent years. Increased bacterial concentration in the raw water may lead to a higher formation of TCM, TCNM, DCAA and TCAA, but not for DCAN, TCAN, 1,1-DCP and 1,1,1-TCP. To achieve a low toxicity in drinking water, it is suggested from this study that chlorine concentration should be kept low, under disinfection contact time of 6h and alkaline condition (pH>8).