Short collagenous peptides cross-linked at their amino and carboxy termini with Lys-Lys-dimer template(s) were synthesized, and the effect of the cross-linking on their stabilities was investigated by thermal denaturation experiments. Two chemoselective ligations were used for the construction of the amino and the carboxy cross-linked peptides. The thermal transition temperature (Tm) and the standard free energies (deltaG(o)) of the cross-linked collagenous peptides increased, and the thermal stabilization effect corresponded to an elongation by two units of the Gly-Pro-Hyp triad. The van't Hoff enthalpy (deltaH(o)) and the entropy (deltaS(o)) values of the cross-linked peptides increased with chain elongation, although the increments were smaller than those of the linear peptides. When the same chain lengths were compared, the deltaH(o) was increased and the deltaS(o) was nearly the same or increased by the cross-linking. These results suggest that the cross-linking of the collagenous peptides with the Lys-Lys-dimer template(s) for stabilization contributes to the enthalpic effect, rather than the entropic effect.