MeBglD2, a beta-glycosidase that is highly activated in the presence of various monosaccharides and disaccharides, was isolated from a soil metagenomic library. MeBglD2 had not only beta-glucosidase activity but also beta-galactosidase and beta-fucosidase activities. MeBglD2 beta-glucosidase activity increased in a cellobiose concentration-dependent manner and was not inhibited by a high concentration of d-glucose or cellobiose. MeBglD2 beta-glucosidase and beta-fucosidase activities were activated by various monosaccharides and disaccharides including d-glucose, d-xylose, d-galactose, maltose, and cellobiose. The saccharification yield of rice straw using Trichoderma reesei cellulase was improved by the addition of MeBglD2. These results show that MeBglD2 can be used to improve plant biomass saccharification, because both substrates and products can activate its enzymatic activity.