The luminescent properties of phosphors are sensitive to their morphologies, particularly to the sizes of phosphor particles. The optimal morphology of the phosphor for the field emission display (FED) is the microsized sphere-like particles. However, less attention has been paid to the phosphors with micron-size controlled particles. In this paper, we reported an improved co-precipitation method to synthesize the red-emitting Y2O3:Eu3+ phosphor with the particle sizes controlled in several microns. The optimum phosphors were obtained at the calcination temperature of 1050 °C and pH=5.5, showing the sphere-like particles with the size distribution from 0.9 μm to 3.1 μm. Compared with the commercial phosphors, such optimum phosphors greatly enhance the cathodoluminescent properties and the corresponding luminescence intensity under the low excitation voltage of 1 kV is increased by 50%. Results indicate an effective way to develop the high-quality FED phosphors.