The marine adhesive polydecapeptide (Ala-Lys-Pro-Ser-Tyr-Hyp-Hyp-Thr-Dopa-Lys)_n(n ca. 10) has been synthesized by coupling reactions, followed by polycondensation. The O-benzyl, O,O′-dibenzyl, and N-ε-2-chlorobenzyloxycarbonyl groups were used to protect the side chains of Ser, Tyr, Hyp, Thr, Dopa, and Lys. The protecting groups were simultaneously cleaved by hydrogen bromide. The bonding strength of the polydecapeptide and other synthetic polypeptides on metals has been measured in water. The bonding strength of the synthesized polydecapeptide exhibited a tensile strength of 28 kg cm^–1 on Fe and a compressive shear strength of 3 kg cm^–2 on Al₂O₃, while high molecular weight poly(Lys)·HBr was found to have the highest tensile strength (123 kg cm^–2) on Fe, and gelatin the highest compressive shear strength (21 kg cm^–2) on Al₂O₃. The factors important for the effective adhesion on metals are discussed.