The Propagation characteristics of a shear horizontal (SH) wave in a trilayer structure having a viscous fluid layer is analyzed front a numerical analysis. Acoustic phase changes under application of electric fields in a nematic liquid crystal cell are, measured using the SH wave. The acoustic phase advances with increasing the applied electric field. This result corresponds with the viscosity change based on a molecular reorientation of the liquid crystal. In dynamic response measurement, the response times in the phase and the optical measurements are different, because the measured area of the acoustic phase is only the vicinity of the glass surface.