Intensity of the (200) peak in the X-ray diffraction pattern of the MgO film increases as N2 is added to Ar gas during MgO deposition. The optimum flow rate ratio of N2 to Ar in order to obtain maximum intensity of the MgO (200) peak is 2 : 5. As introducing N2 gas, no residual nitrogen atoms are found in the MgO films, which are confirmed by AES and ESCA analysis. On the other hand, the TEM dark field image shows that the average grain size of MgO film increases with increasing the flow rate ratio of N2 to Ar. This is due to that the deposition rate of MgO film is decreased with increasing the flow rate ratio of N2 to Ar.