Transparent conducting In 2 O 3 –ZnO thin films were prepared by ultrasonic spray pyrolysis technique. Indium nitrate trihydrate (In(NO 3 ) 3 ·3H 2 O) and zinc acetate dihydrate (Zn(CH 3 COO) 2 ·2H 2 O) were used as precursors and a solvent was 2-methoxyethanol. The thin films, as a function of Zn/(Zn+In) atomic ratio (abbreviated to x), were annealed at 550°C. Oxygen gas was used as both carrier and reactor gas. From analyzing X-ray diffraction patterns, In 2 O 3 phase and ZnO phase were formed at x=0.11 and 0.89, respectively, while homologous phases of In 2 O 3 –ZnO were observed between x=0.5 and 0.67. The resistivity of the thin film increased until x=0.33 and then decreased to be the lowest value (1.47×10 −2 Ωcm) at x=0.5. In the range of x=0.6–1, the resistivity increased again with x. The highest carrier concentration and the highest Hall mobility were 2.02×10 19 cm −3 at x=0.6 and 15.89cm 2 /Vs at x=0.5, respectively. The optical transmittance in the visible region at x=0.5 was 88–92%.