An investigation was undertaken on application of dilute chitosan solutions modified by tyrosinasecatalyzed reaction with 3,4-dihydroxyphenetylamine (dopamine) to adhesion of the low-density polyethylene (LDPE) plates surface-grafted with hydrophilic monomers. Tensile shear adhesive strength effectively increased with an increase in the grafted amount for methacrylic acid-grafted and acrylic acid-grafted LDPE (LDPE-g-PMAA and LDPEg-PAA) plates. In particular, substrate breaking was observed at higher grafted amounts for LDPE-g-PAA plates. The increase in the amino group concentration of the chitosan solutions and molecular mass of the chitosan samples led to the increase in adhesive strength. Adhesive strength of the PE-g-PMAA plates prepared at lower monomer concentrations sharply increased at lower grafted amounts, which indicates that the formation of shorter grafted PMAA chains is an effective procedure to increase adhesive strength at lower grafted amounts. Infrared measurements showed that the reaction of quinone derivatives enzymatically generated from dopamine with carboxyl groups was an important factor to increase adhesive strength in addition to the formation of the grafted layers with a high water absorptivity. The above-mentioned results suggested that enzymatically modified dilute chitosan solutions can be applied to an adhesive to bond polymer substrates. The emphasis is on the fact that water is used as a solvent for preparation of chitosan solutions and photografting without any organic solvents.