Agricultural and forestry wastes abundant in the plant biomass are an important resource of green energy. However, little is known about how to exploit efficiently the resource. In this study, we isolated the CelB gene that encodes the extremely thermophilic cellulose-degrading enzyme from Thermotoga maritime. The enzyme-encoding gene CelB was optimized and reconstructed in N' codes by the code adaptability in Arabidopsis thaliana. Then, the optimized gene (CelB-m) or the recombinant gene (CBD-CelB) was fused with the plant binary vector which harbors the beta-glucuronidase (GUS) gene that was transferred into Arabidopsis, respectively. GUS assay results showed CelB gene ubiquitous expression in transgenic plants. The enzyme-activity assays exhibited that the cellulase activity in the leaves of CelB-m transgenic plants were significantly higher than that of wild-type plants. The highest amount of enzymatic activity obtained was 131.2 U for every gram of fresh leaves in CBD-CelB plants. In addition, the enzymatic activity was stable at the temperature of 90 A degrees C. These results suggested that the ectopic expression of pertinent biomass-degrading enzymes in transgenic plants can degrade effectively the plant biomass and lay a foundation on the application for the transgenic technique to crops.