Greater strength and thermal conductivity of component parts of portable electronic devices are increasingly required due to the increased degree of integration and the shock factor as a result of mobility. In this regard, it is necessary to conduct research to improve the physical properties using crystallized glass or alumina filters. This study focused on the identification of regions where anorthite glass, anorthite crystals, diopside crystals, and alumina phase coexist. It was observed that not only did Al2O3 react with anorthite-system glass and create anorthite crystals in the course of sintering, but it also reacted with the diopside phase and generated MgAl2O4. However, when the average particle diameter of Al2O3 was relatively large, at 3.5 mu m, MgAl2O4 was not created following the addition of 23% Al2O3 or less. As a result of the evaluation of the strength and thermal conductivity, it was found that both physical properties rapidly fell when the 2nd-phase MgAl2O4 was generated.