Measurements were made of the light scattered out of the Corning 7059 glass thin‐film optical waveguide sputtered onto substrates of pyrex glass. The angular distributions of the scattered light can be explained by the waveguide imperfections not only of surface roughness of air‐film‐substrate interfaces but of refractive‐index inhomogeneities. The measured scattering patterns are consistent with the theory taking account of both imperfections, assuming a correlation length ofbx/&lgr; ∼ 0.05 andbz/&lgr; ∼1.0, wherebxandbzare the correlation lengths in the directions perpendicular and parallel to the waveguide surface.