A chito-oligosaccharide (COS) with the number average degree of polymerization (DPn) of 9 was immobilized on poly(vinyl alcohol) (PVA) by crosslinking with a bifunctional compound, N-methylolacrylamide (NMA). The reaction was composed of two successive steps, the reaction of COS with NMA in an acidic medium in the first step and the reaction of the COS-NMA with PVA in an alkaline medium in the second step. The reaction products were characterized by H-1 NMR, differential scanning calorimetry (DSC), and X-ray diffractometry. The relative crystallinity of PVA containing COS side chain (PC) was found to be lower than that of PVA due to the bulky and rigid COS backbones. The tensile modulus of PC film was lower than that of PVA him, but its tensile strength was higher. The antimicrobial activity of PC was excellent in spite of its low COS content. The PC is considered to be a good candidate for a new biomaterial having various functional properties of chitosan coupled with good mechanical properties of PVA.