Single phase, epitaxial, transparent, and p-type CuAlO2films are successfully grown on c-plane sapphire by polymer-assisted deposition. At wavelengths in the range of 400–1000 nm, the optical transmittance of the films is 60–80 %. The energy band gap is 3.6 eV. The as-synthesized CuAlO2 films are highly resistive, with room-temperature resistivity around 105 Ω cm. The resistivity can be reduced to 103–104 Ω cm by post-annealing films in oxygen.