Application of a surface coating to Corning 7059 glass thin‐film optical waveguides has been shown to significantly reduce their scattering loss. Combining the technique of CO2laser annealing of glass waveguides with surface coating, we measure waveguide loss as low as 0.01 dB/cm. By attributing the decrease in attenuation to elimination of the effects of surface irregularities, we were able to identify surface and bulk contributions to scattering losses in the original waveguide. By making such an identification before and after laser annealing, we confirm that CO2laser annealing of glass waveguides reduces both surface and bulk contributions to scattering losses.