Trichoderma reesei cellobiohydrolase I (CBHI) and Cellulomonas fimi cellulase-xylanase (Cex) both have distinct C-terminal cellulose-binding domains which belong to different CBD sequence families. Two fusion proteins comprising a single-chain antibody fragment (OxscFv) against 2-phenyloxazolone fused to the two CBDs (CBDCBHI or CBDCex) were constructed. The binding properties of the fusion proteins were studied on different cellulosic substrates. It was shown that the CBDCex binds the fusion protein to cellulose more effectively than the CBDCBHI; however, once immobilized, both fusion proteins could be eluted from cellulose only with denaturing agents or very low or high pH. Both fusion proteins retained equally well their ability to bind the hapten recognized by their antibody part.