Core/shell microspheres of polymethylmethacrylate coated with Al2O3 or a mixture of Al2O3 and SiO2 nanoparticles have been successfully prepared by a mechanofusion system. The microspheres were then subjected to removal of PMMA by firing in air, followed by sintering at 1600degreesC for 3 h. The shell structure was destroyed after the sintering when the shell layer consisted of only Al2O3. The addition of SiO2 was found to be effective for maintaining the original shell structure, while the shell size expanded slightly and a hole was formed in each hollow microsphere during the removal process of PMMA.