A variety of new inorganic compounds have been prepared by hydrothermal reaction and their crystal structures were determined by single crystal X-ray diffraction or powder neutron diffraction data. They are divided into three groups; i) transition metal oxides, ii) zirconium phosphates and iii) bismuth oxides. Most of new compounds can not be synthesized by high temperature solid state reaction. Particularly some of bismuth oxides prepared by using NaBiO₃·nH₂O as a starting compound exhibited interesting properties such as superconductivity or photocatalysis under visible light. Synthesis, crystal structure and some properties of these new compounds were reviewed briefly.