The purpose of this study was to investigate the performance of a biofilter in which aeration process was not performed while adequate pure oxygen was dissolved into the influent before it was pumped to the biofilter. Two bio-ceramic filters were used in the experiment. The conventional aeration means was used in one bio-ceramic filter (BF-A) and raw water was pumped directly to the filter. At the same time, raw water was oversaturated by pure oxygen before it was pumped to another bio-ceramic filter (BF-B) and aeration was not performed in the filter. It was shown that dissolved oxygen in the influent of BF-B met the demand of microorganism in BF-B and the capability of BF-B to remove pollutants in raw water was superior to BF-A. This result indicated the significance of developing appropriate bubbleless aeration device fitting for oxygenation in biological treatment process of drinking water from the point of view of the biological treatment performance.