[en] Highlights: • Cl₂ decreased algae fluorescence but cells size do not remarkably varied. • O₃ led to more cells with decreased size but less reduction in fluorescence. • Pre-chlorination increased DBP yields detected after coagulation-filtration. • Pre-ozonation decreased total DBP yields detected after coagulation-filtration. • Pre-oxidation affected HAA&chloral precursors more greatly than THM precursors. -- Abstract: Effect of pre-chlorination and pre-ozonation on Microcystis aeruginosa (MA) and Coccomyxa subellipsoidea (CS) as disinfection by-products (DBPs) precursors was investigated after coagulation-filtration. Pre-chlorination considerably decreased the autofluorescence of algae cells but barely influenced cell granularity. In comparison, after pre-ozonation more algae cells were associated with decreased cell size; yet less reduction in the autofluorescence was observed. In MA case, pre-chlorination increased the residual algae density after coagulation-filtration by 132%–146% while pre-ozonation enhanced the algae removal by 26%–28%. In CS case, algae removal was improved by pre-chlorination (32%–45%) and pre-ozonation (7%–45%). Pre-chlorination enhanced the removal of algogenic organic matters (AOM) by coagulation-filtration, especially for tryptophan-like and soluble microbial products. Effect of pre-ozonation on the fluorescence intensity of AOM after coauglation-filtration depended on AOM species and the ratio of [ozone dose]:[algae density]. In both MA and CS cases, chlorine increased the yields of trihalomethane (THM, 25%–78% and 51%–103%), haloacetic acid (HAA, 140%–360% and 167%–233%) and chloral (50%–161% and 68%–108%), respectively. Pre-ozonation decreased the total DBPs yields. For MA-added suspensions, ozone decreased the production of THM, HAA and chloral by 15%–37%, 28%–39% and 60%, respectively. In CS case, chloral yield was decreased by 12%–31% while THM formation was largely unchanged. HAA production varied by ± 1.5 μg/L.