Activated cellulose carrying aldehyde (CHO) and acylchloride (COCl) reactive sites was created by reacting cellulose with dialdehydes, i.e., polyethylene glycol (PEG) diacylchloride and glutaraldehyde (GA), to yield Cell-PEG-COCl and Cell-CHO, respectively. Cellulose fibers and microcrystalline cellulose were readily esterified by PEG diacylchloride to form Cell-PEG-COCl to reach as high as 0.24 to 0.37 mmol aceylchloride per gram cellulose, respectively. The generation of free COOH from PEG diacylchloride reactions was optimized at the lower COCl/OH ratio, where the tendency to half-ester formation was more prevalent than to diesters. Reactions with 8 and 16% GA, generated 0.83 to 1.26 mu mol free aldehyde per gram of cellulose, respectively. The reactivity of the aldehyde groups toward poly(vinyl alcohol) (PVA) hydroxyl was robust, generating cellulose fiber supported PVA hydrogels that could swell up to 62 times. These reactions have shown to be highly effective to create aldehyde functionalized cellulose and demonstrated a simple, yet viable way to support PVA hydrogels for superior swelling and improved mechanical stability. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 2489-2495, 2010