Some perovskite oxides were prepared by the novel low temperature synthesis using a powder mixture including hydroxides and transition oxide gels. Particularly, it was found that BaZrO3 and BaHfO3 could be obtained under 50 degrees C with a high crystallinity. From the results of synthesis, it was found that the products crystallized only when the tolerance factor was larger than 1. It was considered that the tolerance factor of products strongly affects the formation of lattice of perovskite oxides.