The modulation of guided optical waves has been accomplished using an integrated ferroelectric thin‐film structure. LiTaO3was rf sputtered onto 7059 glass in an argon‐oxygen environment. Electrodes for applying the modulation signal were formed by chemically etching an interdigital pattern in gold which was rf sputtered onto the LiTaO3. The observed modulation of guided waves launched in the ferroelectric film can be attributed to the linear electro‐optic effect.