This paper reported following results of an experimental study on the mechanism of shear strength decay of RC members under cyclic load reversals; failure pattern of RC members was classified into two types, i. e., shear failure and bending failure, by separating displacement components. Shear strength decay of concrete under load reversals is brought by the loss of shear transfer by concrete in compression zone. While confinement stress of core concrete by hoops exists, shear strength of concrete is kept about 40% of shear strength of RC members under monotonic load. To prevent shear failure under load reversals, tensile stress of hoops must be kept at least under 80% of its yield strength.