Three quaternary ammonium salts namely 4-amino-laurylpyridinium chloride, 4-benzoylamino-1-dodecylpyridinium bromide, and 4-(1-naphthoyl) amino-1-dodecylpyridinium bromide were employed in antimicrobial finishing of dyed and undyed cotton fabrics. The intermolecular interactions between the dyes and the arminopyridinium salts, and their impact on the exhaustions of salts on the dyed fabrics were discussed. The quaternary ammonium salts could form ionic interactions with sulfonate groups on the dyed cotton fibers, which contribute to higher exhaustion uptakes of the salts and better antimicrobial activities against Escherichia coli of the dyed cotton fabrics compared with that of the undyed sample. However, the washing durability of the antimicrobial functions on the finished cotton fabrics was still low because of easy dissociation of the ionic interactions in water. (c) 2007 Wiley Periodicals, Inc.