Al-doped In2O3-ZnO films were developed and the influence of Al doping in electrical and optical properties of In2O3-ZnO films was investigated. Amorphous and homologous phases appeared with increasing δ=Zn/(Zn+In) ratios. The carrier generation mechanism is discussed for these films. Native oxygen defects are the primary donors for the In2O3-ZnO films. Then the low resistivities of 2–4×10-4 Ω cm were attained within a narrow range of δ=Zn/(Zn+In) in the amorphous phase film. Two wt % (percent by weight) Al2O3-doping decreased the resistivity to 1.5–2.1×10-4 Ω cm. At doping of 3 and 4 wt % Al2O3, film resistivities of 2–4×10-4 Ω cm were attained for a relatively wide range of δ in the amorphous phase due to an increase in carrier concentration at δ=0.3–0.6. However, Al2O3 doping in homologous phase In2O3-ZnO films decreased carrier concentration independently of the levels of Al2O3 doping. Al2O3 doped in the homologous ZnkIn2Ok+3 crystalline films did not act as a donor impurity. The optical band-gap energy for the films deposited above 2 wt% Al2O3 for amorphous film was proportional to Al2O3 content. This is ascribed to lattice distortion caused by Al2O3.