The use of a shear horizontal surface acoustic wave device in measurements of conductivity and pH of liquid is described. The device has two parallel SAW delay lines fabricated on 36° rot Y cut X-prop. LiTaO3. The propagation surface of the one delay line is metallized but that of the other has no metallized area for an acoustoelectrical interaction with a liquid. The conductivity and pH of a liquid are measured by the differential signals of the both delay lines. Some acid and alkali solutions are examined. The SAW sensor is applied to the study of an enzyme-substrate reaction that shows the change in pH.