The cellulolytic-bacterial microflora of the silkworm (Bombyx mori) gut was studied. A facultative anaerobic and cellulolytic mesophilic bacterium determined as Cellulomonas sp. was isolated from silkworm gut at 25°C and 30°C in cellulose agar. The strain generation time was almost 3 h. The highest level of endoglucanase (E.C. 3.2.1.91) [cellulose 1,4-β-cellobiosidase] was observed 6 days after culture.