Thin films of ZrO2SiO2 were deposited by reactive magnetron sputtering and reactive ion beam sputter deposition. The films were fabricated into planar optical waveguides by either ion beam milling or using liftoff lithography. The indices of refraction of the mixed-oxide films were found to be approximately a linear function of composition and were varied from 2.15 to 1.67, The films with >12% SiO2 were amorphous and thermally stable to at least 500 °C. Optical loss measurements on films with high ZrO2 content indicated losses of 3 to 4 dB/cm. © 1989, American Vacuum Society. All rights reserved.