Dissolved organic nitrogen (DON) is currently considered to be one of the most important issues in drinking water field due to its formation of nitrogenous disinfection byproducts. This paper deals with DON concentrations in typical processes of a water treatment plant. The results show that very little DON is removed by these processes. Furthermore, biological activity in some processes can even increase DON concentration and decrease the ratio of dissolved organic carbon/DON, which may pose a risk to drinking water safety.