Poly(ethylene glycol) (PEG) dialdehyde diethyl acetals of different molecular sizes were synthesized and used to generate in situ PEG dialdehydes for the crosslinking of partially reacetylated chitosan via Schiff reaction and hydrogenation of the aldimines. The water-soluble products obtained were instrumentally characterized. Upon freeze-drying, they aggregated to yield insoluble soft and spongy biomaterials, that swelled immediately upon contact with water. When exposed to papain and lipase, at physiological pH values, progressive dissolution of the biomaterials was observed, but no dissolution took place with lysozyme, collagenase and amylase. They were found to be biocompatible towards Caco-2 cells. These crosslinked partially acetylated chitosans seem suitable for medical items when prompt resorption is sought.