Planar and channel optical waveguides have been produced inY‐cut LiTaO3substrates by zinc diffusion from the gaseous phase at 800 °C. Prism coupler measurements on planar waveguides diffused for 6 h indicate effective index changes of 0.0063 and 0.0033 for TE and TM polarizations, respectively, with effective diffusion depths of 3.5 and 3.9 &mgr;m for the two polarizations. Losses in channel waveguides at 0.633 &mgr;m wavelength were 1.0±0.2 dB/cm for TE polarized fields, as compared with 4.7±1.0 dB/cm measured on companion samples produced by the conventional Ti indiffusion process at 1150 °C. Electro‐optic modulation has been demonstrated in channel waveguide interferometers produced by this technique. Based on electron microprobe analysis, a surface Zn concentration of ∼1.3×1021cm−3has been determined.