By means of S-4200 SEM, phase separation of CaO-Al2O3-SiO2 glasses upon application of an electric field is investigated. The experimental results show that externally applied electric field promotes the phase separation of the glass, and it leads to a different size of the droplet phase. In the vicinity of the anode of the glass, the smaller droplet phase is induced compared with the cathode of the glass. The accelerating phase separation of the glass in the presence of an electric field is due to the decrease in the free energy forming a critical nucleus size. The different size of the droplet phase of the cathode is due to the increase in the driving force of nucleation and decrease in the viscosity of the glass compared with that of the anode of the specimen.