YBCO film has been deposited on (100) silicon substrate via ZrO2 film as a buffer layer by the use of microwave plasma MOCVD. In the apparatus, the microwave was converted from TM10 (rectangular) mode to TM01 (circular) mode by a mode converter to make the plasma more active. ZrO2 was selected as a buffer layer to prevent the reaction of deposited YBCO film and Si substrate. Although polycrystalline ZrO2 films are generally obtained by MOCVD, the epitaxial ZrO2 films with (111) orientation were obtained at below 300 degrees C by the use of this apparatus. The film deposited at 300 degrees C for 2 h had a thickness of 90 nm and consisted of small particles with an average size of 50 nm. According to the ESCA measurements, the films were free from carbon, except for the surface. Epitaxial Rims of YBCO with c-axis orientation were deposited on the (111) orientated ZrOz film at 650-700 degrees C for 1 h. The a-axis orientated film was also obtained at 600 degrees C. The YBCO films consisted of small grains with the average grain size of 0.1 mu m and the film thickness was ca. 0.3 mu m. The critical temperature (T-c) and the critical current density (J(c)) of the film obtained at 600 degrees C were 85 K and 1 X 10(5) A/cm(2) (at 77 K), respectively.