Clostridium cellulovorans, an anaerobic bacterium, produces a small non-enzymatic protein called HbpA, which has a surface layer homology domain and a type I cohesin domain similar to those found in the cellulosomal scaffolding protein, CbpA. In this study, we demonstrated that HbpA could bind to cell wall fragments from C. cellulovorans and insoluble polysaccharides, and form a complex with cellulosomal cellulases endoglucanase B (EngB) and endoglucanase L (EngL). Synergistic degradative action of the cellulosomal cellulase and HbpA complexes was demonstrated on acid-swollen cellulose, Avicel and corn fiber. We propose that HbpA functions to bind dockerin-containing cellulosomal enzymes to the cell surface and complements the activity of cellulosomes.