A bioreactor incorporating a slurry-phase reaction was developed for high-rate decomposition of food wastes with an ultimate goal of complete decomposition leaving minimal residue of food wastes when compared to conventional food waste treatment producing composts. In this slurry-phase decomposition, suspended solids in the reactor disappeared with a maximum rate of 7.9 g dry weight dm(-3) day(-1). The changes in dissolved oxygen concentration and pH were closely related to the decomposition of food wastes. The concentrations of nitrate and phosphate in the liquid phase also gradually decreased and disappeared completely at the end of five days of operation. Approximately 82% of carbonaceous compounds in the initial food wastes were decomposed during this 5-day operation. Long-term operation of slurry-phase bioreactors with daily addition of fresh food wastes was successfully carried out for 46 days.