Antimicrobial nonfibrillated lyocell fibers were developed by crosslinking reactions between dialdehyde cellulose and chito-oligosaccharides. Partially oxidized lyocell fibers with sodium metaperiodate were successfully crosslinked with two water-soluble chito-oligosaccharides with different molecular weights by Schiff base formation and were reduced with sodium borohydride. Infrared spectroscopy Measurements showed the characteristic absorption bands caused by the functional groups of each reaction product. The surface chemical compositions of the modified fibers were analyzed with electron spectroscopy. O-1s intensities decreased with the oxidation and crosslinking reaction, whereas N-1s intensities increased with the cross] inking reaction. According to the curve fittings, C-1s spectra were divided into -CH, -CO-/-CN-, -C=O, and -COO- peaks, and their relative peak areas confirmed the reaction results. The degree of fibrillation of the crosslinked fibers decreased with the oxidation levels and chito-oligosaccharide concentrations and increased with the molecular weight of the chito-oligosaccharide. Furthermore, the chito-oligosaccharide-treated lyocell fibers exhibited antimicrobial activity, especially when treated with a chito-oligosaccharide of a low weight-average molecular weight. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 709-714, 2009