Abstract: The nano-crystalline ZnGa₂O₄ spinels were synthesized with GaO（OH） and ZnO by hydrothermal synthesis.The samples were characterized by XRD,SEM,TEM and AFM.The result shows that pH values signifieantly influence the crystal-phase and size of ZnGa₂O₄ prepared by the hydro thermal reaction.When pH is bigger than or equal to 7.5,the pure ZnGa₂O₄ nano-powder may be obtained.The lattice parameter increases with the pH increasing.The sizes of samples are 6-11nm,and emission peak of ZnGa₂O₄ is at 450nm.The shape of samples is quite perfect,GaO（OH） is needlelike nanorystal particle and ZnGa₂O₄ is cubic or octahedral in appearance.