We have prepared the gallium oxide (β-Ga2O3) nanomaterials from gallium and oxygen by thermal evaporation in the argon atmosphere and researched their photoluminescence (PL). X-ray diffraction (XRD) revealed that the synthesized products are monoclinic gallium oxide, and its morphology as observed by the scanning electron microscope (SEM) revealed that Ga2O3 nanobelts with breadth less than 100nm and length of several micrometers are synthesized under low oxygen pressure, while nanoparticles are synthesized under high oxygen pressure. Room-temperature photoluminescence under excitation of 325 nm shows that the β-Ga2O3 nanostructures have stable emission at 516 nm, which may be related to the defects such as the oxygen vacancies and the gallium-oxygen vacancy pairs.