Torsional stiffness of its steel‐cord‐reinforced belt structure affects various characteristics of a radial tire, particularly when it is operating at a camber angle other than zero. We analyzed the torsional stiffness of the belt, with consideration of interply shear deformation, by modeling it with a laminated biased composite strip of unidirectional cord‐reinforced rubber (UDCRR) layers. The coupled torsional‐extensional deformation of the belt was shown to vanish at the particular bias angle of 54.7°. It is pointed out that the torsional rigidities of constituent steel cords, which were not considered in the classical lamination theory, could increase the twisting stiffness of the belt structure over that predicted by the conventional lamination theory. A test specimen of low aspect ratio was fixed at both ends under torque loading for the tests. Experimental results of the torsional stiffness together with the coupled torsional‐extensional strain agreed well with the analytical results.