As the essential target of disinfection, bacterial materials should also be considered as one type of disinfection by-products precursors (DBPs). This study investigated the disinfection by-products formation potential (DBPFP) of bacterial materials during chlorination and chloramination. The bacterial materials were harvested from mature biofilm developed in remineralized desalinated seawater with different carbon sources. It was observed that calcium and magnesium which were added to desalinated seawater for remineralization could enhance DBPFP of bacterial materials, with magnesium being more effective. The enhancement effect was related to the ability of calcium and magnesium to shift low molecular weight fractions of bacterial materials to more hydrophobic and larger molecular weight fractions. Bacterial materials developed with humic acid as carbon source contained more hydrophobic and larger molecular weight fractions, hence had higher DBPFP than bacterial materials developed with acetate. DBPs yields of bacterial materials were lower than that of NOMs precursor during chlorination, but during chloramination DBPs yields of bacterial materials were higher. The extracellular polymeric substances (EPS) matrix had higher DBPs yield than biofilm cells. Polysaccharide was more likely to be the main DBPs precursor in the EPS matrix.