We describe the reactive ion etching of LiNbO3 in gas mixtures containing CCl2F2, CF4, O2, and Ar. The effects of gas composition and pressure, in the range 1–10-μm total pressure are discussed. Because it is possible to replicate fine features (∼2000 Å) with control of etch profiles, we expect the process to be used for three-dimensional patterning of LiNbO3 for electro-optic and acoustic-optic devices.