Natural organic matter (NOM) fractions in the raw waters collected from the Huangpu and Yangtze rivers were separated according to their hydrophobicity and molecular weights (MWs) using resin adsorption (RA) and ultrafiltration (UF), respectively, to investigate the formation potential of carbonaceous disinfection by-products (C-DBPs), nitrogenous DBPs (N-DBPs) and iodinated DBPs (I-DBPs) after chlorination and chloramination for each fraction. The removal of C-, N- and I-DBP precursors in each process by the Minhang No. 2 and Yangshupu drinking water treatment plants (DWTPs) was also studied. After chlorination, hydrophobic NOM with MW < 1 kDa contributed the most to the formation of C-DBPs, whereas for chloramination, hydrophilic NOM with MW < 1 kDa contributed the most to the formation of C-DBPs in both raw waters and trihalomethanes (THM4) were the dominant components. Most of the N-DBPs were formed from different NOM fractions in the Huangpu (hydrophilic and MW > 10 kDa fractions) and Yangtze (hydrophobic and MW < 1 kDa fractions) rivers after chlorination. However, after chloramination, the formation of N-DBPs was distributed relatively evenly among the three hydrophobic fractions. Additionally, N-DBP formation decreased with increasing MW for the Huangpu river, and for the Yangtze river, MW fractions > 10 kDa exhibited higher reactivity. In both rivers, the hydrophilic NOM contained the majority of I-DBP precursors. After chlorination, most of the I-DBPs came from MW fractions >10 kDa and <1 kDa in the Huangpu and Yangtze rivers, respectively, whereas after chloramination, the MW < 1 kDa fraction was the major source in both rivers. This study also found that conventional water treatment processes could not remove DBP precursors effectively, and the control over DBP formation after chloramination was more difficult than after chlorination, especially for I-DBPs. (C) 2014 Elsevier B.V. All rights reserved.