Objectives: In order to increase cellulose degradation, cellulase was expressed in this study. Literature Review: Cellulose is the most abundant organic carbon source on Earth; its enzymatic hydrolysis will be very useful for bioenergy production and resource recycling. Methods: Cellobiohydrlase I (CBH I) gene was amplified from genomic DNA of Trichoderma koningii and inserted into pGAPZα A plasmid to construct the vector of pGAPZαA-CBH I. It was linearized and transformed into Pichia pastoris by electroporation. The recombinant Pichia pastoris was selected and incubated with YPD medium for cellulase secretion. Results: The result showed that CMCase and avicelase activity in the supernatant was 1.1798 U/mL and 0.1276 U/mL, the molecular weight of the expressed protein was 53 kDa determined with SDS-PAGE analyses, and the optimal temperature and pH of the expressed cellulase were 45?C - 50?C and 4.5 - 5.0, respectively. Conclusion: Cellulase gene from T. koningii has been successfully cloned and expressed in Pichia pastoris.