This study investigated the formation behavior of two CDBPs, namely THMs and HAAs, in a treatment plant and the distribution network of Macau. Concentrations of the four species of THMs and the six species of HAAs were monitored at different stages of the treatment process and at two separate points in the distribution network during February 2006 to January 2007. The results show that the mass concentration of THMs was generally higher than that of HAAs in treated water with a ratio ranging from around 1:1 to 2:1. The results suggested that two steps, pre-chlorination and coagulation, performed in the treatment process influenced the formation of CDBPs in the plant. The CDBPs formation was found to continue in the distribution system with the concentration of THMs increasing faster. The effect of temperature on the formation of HAAs was found to be more significant than on that of THMs. In an alkaline condition, both THMs and dihaloacetic acids were easier to form but the concentration of some trihaloacetic acid decreased.