The cellulose-hydrolyzing strains, Sphingomonas paucimobilis MK1 and Bacillus circulans MK2, were separated from soil and were grown together in a single culture plate. Growth B. circulans MK2 in liquid culture required symbiosis with S. paucimobilis MK1. Biological pretreatment with the combined strain suspension after the liquid culture improved enzymatic hydrolysis of office paper from municipal wastes. Sugar recovery by S. paucimobilis MK1 (51%) was 1.4 times higher than that of the untreated sample (30%) and in the strain combination with B. circulans MK2, recovery was further improved by 2.5 times (75%). The sugar recovery in maximum condition was enhanced up to 94% for office paper. Furthermore, biological pretreatment effects were confirmed for more than 1 day less time. In X-ray diffraction patterns for the crystallinity of cellulose in office paper changed after biological pretreatment, the crystallinity was increased in comparison to that in untreated paper. The mechanism of biological pretreatment effect was explained by the fact that the strain acted as an endoglucanase, which hydrolyzes amorphous areas randomly.