Effect of microwave induced O 2 - and Ar-plasma on characteristics of YBa 2 Cu 3 O 7 - x (YBCO) superconducting films deposited by pulsed laser deposition technique (PLD) was examined. Surface roughness of the films was greatly improved at the presence of O 2 -plasma, but was substantially degraded at the presence of Ar-plasma. Epitaxial-like YBCO superconducting films with c-axis perpendicular to the films' surface and with a- and b-axes aligned in films' plane were obtained on (100) MgO substrates. They have onset of transition temperature at T c = 90 K and zero at T c0 = 86 K. The mechanism for the improvement in this process was investigated by optical emission microscopy (OEM). The production of abundant atomic oxygen in microwave induced oxygen plasma that enhances the surface reaction kinetics is believed to be the main factor for improving surface smoothness of the films.