A liquid jet head, comprising: an actuator substrate comprising: a plurality of grooves aligned in parallel to each other in a surface thereof; partition walls separating the plurality of adjacent grooves from each other; and drive electrodes placed on both side surfaces of each of the partition walls; a cover plate bonded onto the surface of the actuator substrate so as to cover the plurality of grooves; and a nozzle plate comprising nozzles communicating to the plurality of grooves, the nozzle plate being bonded onto an end surface of the actuator substrate, wherein the actuator substrate comprises a drive region for driving the partition walls so as to deform the partition walls, and for causing liquid filling the plurality of grooves to jet from the nozzles, wherein, in the drive region, each of the partition walls is made of a piezoelectric material on a top surface side situated above substantially half a height from a bottom surface of each of the plurality of grooves to a top surface of each of the partition walls, and made of a low-permittivity material, which is lower in permittivity than the piezoelectric material, on a bottom surface side situated below substantially half the height, wherein, in the drive region, each of the drive electrodes is placed so as to extend across each side surface of each part of the partition walls made of the piezoelectric material and onto each side surface of each part of the partition walls made of the low-permittivity material, and characterised in that the drive electrodes are shaped so that ranges, in which the drive electrodes are formed on the plurality of partition walls made of the low-permittivity material, gradually change from one end to another end of the actuator substrate. an actuator substrate comprising: a plurality of grooves aligned in parallel to each other in a surface thereof; partition walls separating the plurality of adjacent grooves from each other; and drive electrodes placed on both side surfaces of each of the partition walls; a plurality of grooves aligned in parallel to each other in a surface thereof; partition walls separating the plurality of adjacent grooves from each other; and drive electrodes placed on both side surfaces of each of the partition walls; a cover plate bonded onto the surface of the actuator substrate so as to cover the plurality of grooves; and a nozzle plate comprising nozzles communicating to the plurality of grooves, the nozzle plate being bonded onto an end surface of the actuator substrate, wherein the actuator substrate comprises a drive region for driving the partition walls so as to deform the partition walls, and for causing liquid filling the plurality of grooves to jet from the nozzles, wherein, in the drive region, each of the partition walls is made of a piezoelectric material on a top surface side situated above substantially half a height from a bottom surface of each of the plurality of grooves to a top surface of each of the partition walls, and made of a low-permittivity material, which is lower in permittivity than the piezoelectric material, on a bottom surface side situated below substantially half the height, wherein, in the drive region, each of the drive electrodes is placed so as to extend across each side surface of each part of the partition walls made of the piezoelectric material and onto each side surface of each part of the partition walls made of the low-permittivity material, and characterised in that the drive electrodes are shaped so that ranges, in which the drive electrodes are formed on the plurality of partition walls made of the low-permittivity material, gradually change from one end to another end of the actuator substrate.