The purpose of this study was to evaluate the dentin bond strength for demineralized dentin in resin composite restoration with colloidal platinum nanoparticles (CPN). CPN was used as a pretreatment material for one-step adhesive system. Shear bond strength of sound dentin and demineralized dentin were measured by subdividing the concentration and application time of CPN. As a result, both sound and demineralized dentin, the highest bond strength was shown under the condition that 1% CPN and phosphoric acid were mixed (phosphoric acid concentration 35%), applied for 1 second and washed with water. And in fracture modes, under the condition that the highest bond strength was recognized, many cohesive failure within dentin were observed especially with demineralized dentin. It was suggested that CPN is effective in improving the bond strength of sound and demineralized dentin in resin composite restoration. More research is required to determine detailed the morphological evaluation and long-term adhesive durability.