A lithium niobate integrated-optic voltage sensor with variable sensing ranges is realized, which consists of a Mach-Zehnder interferometric wave-guide with an array of buried electrodes. The buried electrodes are fabricated by wet etching of proton-exchanged lithium niobate. In this sensor, the sensing range is almost linearly controlled by simply changing the electrode gap and length. Thus the whole sensing range is effectively extended by integrating a number of electrodes which give different sensing ranges. A sensor with three variable sensing ranges is fabricated and its overall sensing range covers 7 mV to 400 V. (C) 1998 Elsevier Science B.V. All rights reserved.