The purpose of this study was to evaluate the shear bonding strength and leakage of heat-polymerized denture base resin to titanium-aluminum-niobium (Ti-6Al-7Nb) and cobalt-chromium (Co-Cr) castings using four adhesive systems; three adhesive primers (Metal Primer II, Metal Link, MR. Bond) and one heat-polymerized adhesive resin containing 4-META (Metadent). The resin tab was heat-polymerized directly with or without the primer. Shear bonding strengths and dye penetration distances were determined before and after 10,000 times of thermocycling. The results were analyzed with three-way ANOVA and Tukey's comparison (p<0.05). Thermocycling significantly decreased bonding strength and promoted dye penetration. However, with the application of adhesive systems, post-thermocycling bond strength was significantly improved and dye penetration was inhibited. The bonding strength of Ti-6Al-7Nb was significantly smaller than that of Co-Cr, but the difference was marginal. These results suggested that the examined adhesive systems significantly improved the bonding efficiency of heat-polymerized resin to Ti-6Al-7Nb and Co-Cr alloys.