Abstract: Using analytically pure Bi₂O₃ and Dy₂O₃ as raw materials,the Bi_0.75Dy_0.25O_1.5 precursor was prepared by the reverse titration chemical coprecipitation method.By thermogravimetry-mass spectrum (TG-MS) analysis,the results show that the components of the precipitation are BiOOH and Dy(OH)₃ with little BiONO₃ and Bi₂O₂CO₃.After calcining the precursor at 500℃ for 3 h,β-Bi_0.75Dy_0.25O_1.5 could be obtained and its average grain size is 16.02 nm by the Scherrer formula from X-ray diffraction (XRD) analysis.X-ray fluorescence (XRF) analysis shows that the ratio of Bi/Dy extremely approaches to the theoretic stoichiometric ratio.Transmission electron microscope (TEM) analysis results show that the particles size is less than 20 nm in good dispersion.The mechanism of preparation reaction was studied by thermodynamic analysis.