Abstract: Nanocrystalline CoFe₂O₄ ferrite was successfully prepared by the spraying-coprecipitation method.The effect of temperature on microstructure and magnetic properties was investigated.The results show that uniform and fine nanocrystalline CoFe₂O₄ ferrite powders are obtained by the spraying-coprecipitation method.The grain size is about 29 nm calcined at 600℃ for 1.5h.There are a few agglomerates with average sizes below 100nm.The specific saturation magnetization of nanocrystalline CoFe₂O₄ ferrite increase with the calcining temperature of specimens at room temperature,and Ms is 88.6 A·m²·kg^-1 as the calcining temperature is 850℃.When the grain size is 29nm,the maximal coercivity Hc of nanocrystalline CoFe₂O₄ ferrite arrives at 64.5kA·m^-1,then it decreases with the increase of the grain size.The results may be attributed to the effect of grain size in nanocrystalline magnetic materials.