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Purpose: This study compared the surface hardness (Vickers) and microstructural characteristics between a type IV stone with and without die hardening treatment, a polyurethane die material. Methods: Materials used were a type stone(MG Crystal Rock), two die hardeners (Hardening bath, Epox-it), and a polyurethane resin material(Polyluck). Six specimens per group were prepared according to manufacturer’s directions. The prepared specimens were tested by means of hardness test, one-way ANOVA analysis, scanning electron microscopic(SEM) observations and energy dispersive spectroscopic(EDS) analysis. Results: In the hardness test and its statistical analysis, there was no significant difference in the surface hardness between a type stone and type stone with die hardener coating, type stone mixed with an epoxy like material instead of water. In contrast, polyurethane resin material exhibited significantly greater surface hardness than other specimen groups (p<0.05). Conclusion: By considering the results of the hardness test, SEM observations and EDS analysis, although the die hardeners on type stone did not show remarkable improvement in surface hardness, the die hardener coating on the surface of type stone material did show decrease of microporous and improvement of surface defects.