The propagation characteristics of the pure SH (horizontal shear) mode piezoelectric surface acoustic wave (SAW) on rotatedY-cuts about theZ-axis of potassium niobate(KNbO3)are theoretically analyzed. The results show that there exists a SH mode SAW which has a velocity lower than the piezoelectrically inactive Rayleigh mode SAW for most of the rotated cuts. Differing from the so-called Bleustein-Gulyaev wave in 6 mm crystals, the particle displacement of the SH mode SAW on the metalized surface ofY-cutKNbO3decays with slow oscillation as a function of depth from the substrate surface, while that on the free surface oscillates with a slight decay. The electromechanical coupling factorK2ranges from a very large value of 0.53 to a relatively small value of 0.026, depending on substrate orientation. ©1997 American Institute of Physics.