ABSTRACT The conventional elastoplastic model premising that the interior of yield surface is a purely elastic domain is incapable of describing the plastic deformation by the rate of stress inside the yield surface. Thus, it is inapplicable to the description of cyclic loading behavior. Besides, the traditional elastoplastic model is independent of the stress rate component tangential to the yield surface. Therefore, it predicts an unrealistically high stiffness modulus for nonproportional loading process deviating significantly from proportional one. The extended tangential-subloading surface model proposed by Hashiguchi and Tsutsumi (2001) would be capable of describing the cyclic loading behavior and the inelastic strain rate induced by the stress rate component tangential to the subloading surface. In this article, the extended tangential-subloading surface model is applied to the prediction of deformation behavior of sands subjected to various loading ranging from proportional to cyclic nonproportional loading. The validity is verified by comparing with the various test data. Then, it is revealed that the incorporation of the strain rate due to the stress rate component tangential to the subloading surface is of importance for the description of nonproportional loading behavior.