The relationship between fracture strength and crystallization in castable glass-ceramics was studied using castable glass-ceramics which contained crystalline apatite and magnesium titanate. Bending strength was increased with increases in crystal phases; 90, 124, 122 and 162MPa were recorded for as-cast specimens and specimens cerammed at temperatures of 905°, 925° and 945°C, respectively. The results of bending tests suggest that the crystallization of magnesium titanate is more effective than that of apatite in increasing the strength of glass-ceramics. Fracture toughness in specimens reheated at 905°C was doubled compared with as-cast specimens. The apatite particles precipitated during ceramming treatment were thought to be an important factor in increasing both the fracture toughness and crack pinning effect.