This paper describes experimental studies on in-plane scattering of TE-polarized light in titanium-diffused Y-cut LiNbO3optical waveguides as a function of the diffusion process parameters of time, temperature, and the initial film thickness. The dependence of surface roughness on the waveguide fabrication parameters is also described. It has been found that as diffusion time and temperature are increased, in-plane light scattering firstly decreases but then eventually increases. The eventual increase in in-plane scattering is, apparently, because of growth of subsurface waveguide defects. From these studies, a reasonably consistent interpretation for the dependence of the quality of the optical waveguide on the waveguide fabrication parameters has emerged.