Soluble microbial products (SMPs) can act as a disinfection byproduct (DBP) precursor besides natural organic matter (NOM) when source water is polluted by biologically treated wastewater effluent that has SMPs as its main component. Influential factors of SMPs as a DBP precursor were investigated in this study. Model feed substrates were biologically incubated to simulate the biological treatment of wastewater organics, and the SMPs produced were chlorinated according to the standard procedure to study the DBP formation potential (DBPFP) of SMPs. Feed chemical type is a crucial factor affecting SMP production and the following DBP formation. SMPs from four kinds of model feed substrates with the same initial organic carbon concentration produced DBPs with a wide range from 196 to 684 mu g L-1 and also different DBP formation properties. Different organic substrates would facilitate the growth of different microbial species, which produce SMPs with varied levels and chemical structure and subsequently different DBP formation characters. For the environmental factors, an anaerobic condition showed a significant effect, producing extremely high chloral hydrate up to about 2000 mu g L-1, probably due to the production of volatile fatty acids. Different incubation conditions can not only bring about different levels of SMPs and DBPs, but also SMPs with different DBP formation feathers.