Micrometer-sized spherical single crystal particles of a perovskite oxide based on Ca0.40Sr0.60Ti0.95Zr0.05O3 were prepared from a pulverized powder by flame fusion method. The obtained particles are polyhedrons exhibiting 6 quadrate planes, 8 octagonal planes and 8 triangular planes. Semplice electron diffraction patterns corresponding to orthorhombic structure were obtained for the whole thin section of a particle from different radiation directions, indicating that the particle is single crystal. Changes of the morphology, structure and crystallinity of particles were observed by SEM and TEM to investigate the formation mechanism of the particles. It is revealed that a pulverized particle melts in the flame and solidifies to form an as-fused spherical particle which is composed of an amorphous shell and a crystal core. The crystal core acts as a crystal nucleus in the sequential heat-treating process and finally grows to a single crystal above 1150°C.