We present herein a mild and rapid method for the modular functionalization of polysaccharides. Several ene-functional charged and neutral polysaccharides, that is, hyaluronic acid and dextran, were prepared by esterification of the hydroxyl groups with pentenoic anhydride. The modified polysaccharides were then reacted with six model mercaptans under UV light, leading to linear polymers modified with hydrophobic groups, peptides, or oligosaccharides as well as chemical hydrogels. The thiol-ene coupling reactions were found to proceed with high efficiency in short reaction times and with nearly no degradation of the polysaccharide backbone. Moreover, they were carried out in aqueous media, without the use of any metal catalysts, enhancing the attractive nature of this process. Notably, we investigated whether it is feasible to prepare cell-responsive hydrogels by sequential bioconjugation and cross-linking of the polysaccharide backbone with a bioactive peptide and poly(ethylene glycol)-dithiol, respectively. All together, these results highlight the potential of this coupling strategy for the modular functionalization of polysaccharides under click chemistry-like conditions. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012