Crystal structures of a β-glucosidase from the thermophilic bacterium C. saccharolyticus (Bgl1) and its complex with glucose were determined at 1.47 and 1.95 Å resolution, respectively. Comparison of Bgl1 with sequence or structural homologues showed that Bgl1 is quite similar except for two regions, one of which seems to be a unique insertion of residues that is only present in Bgl1.