Tensile stress is applied to the specimens of polymethyl methacrylate (PMMA) andpolystyrene (PS), using a mechanical device composed of screws and a lever, and its effect to the ultrasonic velocity is observed by water immersion ultrasonic sing-aroundmethod for both compressional wave and shear wave. The incidence angle is set to be zero for the compressional wave, or to be the angle appropriately above the critical angle of the compressional wave for the shear wave. Relative ultrasonic velocity varia-tion (RUVV) due to applied stress is linear for all cases, and the effect of RUVV for theshear wave is larger than that for the compressional wave. Next, mechanical anisotropy of injected polypropylene (PP) plate and burned extruded porous machinable ceramic plate are investigated by the similar inclined water immersion method. The relative ultrasonic velocity difference (RUVD) of the injected polypropylene plate ranges up to about 9%.