Core-shell-type composite powders were prepared by hydrolysis of titanium tetraisopropoxide or tetraethyl orthosilicate in a dispersion of core particles adsorbed with water in hexane. Microporous cells could be made of the composite powder dissolved within the core particles in acetic acid solution. The content of titania in BaCO3-TiO2 composite powder was controlled by the amount of water adsorbed. The pore volume of the microporous cell changed with the content of titania. BaCO3-TiO2 composite powder was heated at 600 degrees C for 10 h and barium ions in the core particles were diffused to titania. Thus, microporous cells composed of the BaTiO3 ultrafine particles were prepared.