To provide a photocrosslinking polysaccharide excellent in barrier effect and degradability which are necessary characteristics for medical materials, and to provide a photoreactive polysaccharide for producing the same and a medical material comprising the photo crosslinking saccharide.

This photoreactive polysaccharide includes therein a covalent bonding of a polysaccharide and glycidyl ester expressed by the general formula (1) or (2). [In the formula, R1-CO- or -OC-R2-CO- shows photoreactive residues of a photoreactive compound having carboxyl groups or unsaturated carbon double bonds in molecules for each respectively. However, in the case when the polysaccharide is heparin, R1-CO- is not acryloyl group and methacryloyl group].