Fermentations of cellulose were carried out using rumen microflora. Butyric, propionic, acetic, and traces of formic acids were produced from the cellulose fermented. When peptone was present and the pH of the mash was maintained at 6.5 and the end products of fermentation were removed continuously by a dialysis ion exchange system, 84% of a 4.12% cellulose suspension was fermented in 72 hr. at 40 °C. Fermentations using rumen organisms might become a means of utilization for low forms of wood waste.