In the present work we investigated the applications of chitosan as a bubble surface modifier in the coagulation dissolved air flotation (DAF) process for river water treatment. Zeta potentials of the residual colloidal particles in floated water and other typical water quality indexes measurements reinforced the fact that micro-bubble surface was successfully modified by dosing chitosan in a saturation system. The flotation efficiencies of both natural organic matters (NOM) and particles were obviously enhanced via chitosanmodified bubbles and the effects became more remarkable after the pH of saturation water was adjusted from 7.0 to 5.5, especially for NOM removal. Moreover, the influence of chitosan on DAF performance, as a coagulant aid, was also evaluated. The coagulation-aiding effects of chitosan were equal to acting as a bubble modifier at pH 7.0, but less efficient than the bubble modification DAF at pH 5.5. In addition, the effects of molecular weight (MW) and deacetylation degree (DD) of chitosan on its performance in both dosing strategies were discussed in detail. These findings highlight the advantages of bubble surface modification in surface water treatment and provide an alternative for DAF process optimization.