A method is presented by which not only interference can be induced between two modes whose polarization directions are mutually orthogonal, i.e., between the so‐called Rayleigh‐ and Love‐type modes, but also the strength of the interference can be controlled electrically. It is shown that by applying this method electrically tunable polarization conversion can be obtained along some properly prepared acoustic surface waveguides of thin‐film type. As such waveguides, two examples are considered, each of which is composed of a properly oriented thin &agr;‐quartz film either on a fused‐quartz or on a fused‐rutile substrate, and the basic properties of the polarization conversion are calculated. The applicability of this phenomenon to some practical devices is also discussed.