This study attempted to investigate the relationship between the floc size and efficiency of a DAF (Dissolved Air Flotation) method using a PDA (Photometric Dispersion Analyzer), which is used to monitor floc generation via on-line access. This study applied actual measurements to investigate how the size of bubbles affected the flotation velocity, and introduced similar results to the theoretical flotation velocity reported in the literature. The results were found to play a role in improving the reliability in the evaluation of the flotation velocity of floc-bubble aggregates. From the results of the evaluation of the electrostatic characteristics for application to DAF treatments, the amount of coagulants was determined on the basis of the zeta potential value, which had to be controlled in the order of +2 similar to + 5mV to improve the treatment efficiency. The results of the rapid mixing intensity test using a PDA demonstrated that G value of 900 sec(-1) for 1 similar to 3 sec provided excellent treatment efficiencies in a DAF process. In addition, from the results of the flocculation test based on the flocculation index, the flocculation combination of 70/50 sec(-1) gave reasonable results for DAF operation.