Superconducting thin films of Y-Ba-Cu-O were prepared on single-crystal MgO (100) substrates by the mist microwave-plasma chemical vapour deposition (MPCVD) using an aqueous solution of metal nitrate. The growth rate was observed to be controlled by the concentration of metal nitrate in the solution. The X-ray diffraction patterns showed that the prepared films consisted of 123 phase with c-axis orientation perpendicular to the substrates. The dependence of T-c-zero (zero resistance) of films on the microwave power was investigated. In addition, the effect of the ozone on the preparation of films was investigated. The maximum T-c-zero (84 K) of as-deposited films was obtained at a metal concentration in the solution of 0.50 mol l(-1), a microwave power of 300 W and an ozone concentration in oxygen gas of 3.0%.