The aim of this study was to determine the biaxial flexure strength of a commercially available dental pulp capping or cavity liner material, mineral trioxide aggregate (MTA). MTA and a conventional pulp capping material, calcium hydroxide, were used in this study. Each material was prepared into a disk-shaped specimen. Those specimens were stored in 100% humidity atmosphere at 23 or 37°C for 3 or 24 h. Six specimens in each condition were used for the biaxial flexure test using a piston-on-three-ball according to ISO-6872. Surface pH values were determined. The biaxial flexure strengths of MTA after setting in 24h were larger than those of Dycal (p <0.01). pH value of MTA was higher than that of Dycal. These results indicated that MTA was clinically usage material.