Copoly[LysLys(Cou)] containing epsilon-7-coumaryloxyacetyl-L-lysine [Lys(Cou)] residues were synthesized by the N-carboxyanhydride method. When the aqueous solutions of copoly[LysLys(Cou)] containing 5-10 mol % of Lys(Cou) are irradiated by light, the photo-cross-linking reaction proceeds slowly between coumarin moieties in the side chains to give a cis head-to-head cyclocoumarin, and after 6-24 h the solutions become transparent hydrogels. The gels exhibit solvent-induced reversible expansion and contraction behavior in water and in ethanol. The biodegradation of the hydrogels by some proteolytic enzymes and soil filamentous fungi has been investigated using photo-cross-linked copoly[LysLys(Cou)] gels. The photo-cross-linked copoly[Lys(90-95)Lys(Cou)10(-5)] gels are degradable by trypsin and protease type XXIII or two microorganisms, Aspergillus oryzae and Penicillium citrinum, suggesting potential for a controlled biodegradation by the different cross-linking densities in the gel matrixes upon the controlled irradiation.