Optical waveguide structures have been fabricated on polysilicon-on-insulator. Structural and optical properties of the waveguides are studied by X-ray diffraction, atomic force microscopy, scanning electron microscopy, and transmission measurements. Reasons for the waveguide loss are discussed. It is found that surface roughness can be responsible for a waveguide loss of more than 60 dB cm−1 and that additional loss mechanisms probably exist. Methods of smoothing the surface are discussed.