Ceria nanoparticles were facilely synthesized by a molten NaOH-KOH hydroxide flux method with the precursor of Ce(NO3)3·6H2O under different conditions in alumina crucibles or Teflon-lined stainless steel autoclave. The XRD patts and TEM images show that both the crystal and particle sizes of synthesized nanoceria are around 10 nm. XPS results reveal that the nanoceria obtained in alumina crucible has a Ce3+fraction of 17.1％which is higher than that of ceria synthesized in the Teflon vessel, the FTIR spectra of nanoceria prepared in alumina crucible show a stronger intensity of O-H stretching mode. UV-DRS and PL spectra results show that the nanoceria synthesized in alumina crucible with a calculated band gap of 2.9 eV has a wider responding light wavelength and a lower photogenerated electron-hole recombination rate, due to a higher concentration of oxygen vacancies (Ce3+ ％). The photocatalytic results show that the degradation ratio and rate of the Rhodamine B (RhB) solution with the nanoceria synthesized in alumina crucible are 98.39％ and 0.02919 min-1, both of which are larger than those of the ceria obtained from Teflon vessel. This method proves to be a simple and scalable way to synthesize nanoceria with rich oxygen vacancies and high photocatalytic activity.