Hollow glass microspheres named expanded perlite have been prepared from perlite, but the size is usually above 20 mu m. Recently fine microspheres with low density are desired. In the conventional preparation method, it is difficult to produce fine expanded perlite with particle size under 20 mu m because the water contained in finely milled perlite particle, which is the origin of foaming, is evolved during heating process. Fluidized sand-bed furnace is a useful tool to heat the fine particle rapidly. Using the rapid heat furnace fine expanded perlite with particle size under 15 mu m and bulk density under 0.5 g/cm(3) is prepared successfully. Foaming conditions are discussed by water contents and foaming temperatures. Existence states of water are interpreted by temperature-program med desorption method and FT-IR spectrum.