A bacterial strain named as WH-1 that can degrade cellulose was isolated from the rumen of the Mongolia sheep. The isolate was identified as Butyrivibrio fibrisolvens based on phenotypic and morphologic properties, the G+C mol% content of DNA and the 16S rRNA gene sequence analyses. In addition, the phylogenetic analysis of the 16S rRNA sequence also indicated that the isolate grouped closely with other members of Butyrivibrio fibrisolvens. The primary factors affecting the degradative ratio of cellulose were examined. The highest degradative ratio of filter paper reached 16.81%±2.99% under the conditions of 37°C, pH 7.0, inoculum size being 25%, and the percentage of cellobiose in total carbon sources being 20% within 72 hours of fermentation.