Abstract:Dissolved organic nitrogen (DON) was the main precursors of toxic N-DBPs, and the removal effect of DON was unknown for conventional water treatment process (CWTP). Variation of existence and molecular composition of DON in Huangpu River and the Yangtze River and the removal effect in CWTP was investigated. The results showed that the small molecular (< 5kDa) and hydrophilic organic matters dominated the composition of DON, DOC and UV254 in both two kinds of raw water. In Huangpu River, both autochthonous and allochthonous NOM sources were found. However, the autochthonous sources dominated NOM sources in the Yangtze River. As the result of linear regression analysis of DON and regular water indexes, DON was moderately correlated to DOC with coefficient of 0.59 in Huangpu River and 0.52 in Yangtze River. DON was also correlated to UV254 with coefficient of 0.74 and 0.51 respectively. The DON removal rate by CWTP in the Huangpu River (40.0%) was higher than Yangtze River (16.7%). The great limitation of DON removal by CWTP indicated that the technology of enhanced conventional and advanced water treatment must be applied by the drinking water plants.