Estimated values in previous study were applied to various wool/polyester blend yarns which made with different blend ratios. and then compared and discussed with experimental results. It was shown how the yarn twist and blend ratios in the spun blend yarns affect the torsional hysteresis behavior. And the contributions of interfiber friction by calculating energy loss and coercive couple in torque-torzion hysteresis curve were discussed. Specific torsional rigidity of a spun blend yarn was linearly increased with increasing yarn tension and the extrapolated specific torsional rigidity was adopted by specific net yarn torsional rigidity. The effect of blend ratio on the net specific torsional rigidity of spun blend yarns was exactly shown in the region from 30$^{circ}$ to 35$^{circ}$ of yarn surface helix angle. And the specific net yarn torsional rigidity was decreased with increasing blend ratio of polyester fiber. The maximum specific net torsional rigidity of blend yarns was obtained with increasing the surface helix angle of the yarn. The trend was the same as tensile modulus(E) and bending rigidity(EI) Torsional hysteresis energy due to the interfiber friction of constituent fibers and the coercive torque due to initial resistance of constituent fibres by the torsional deformation were also increased with increasing yarn tension. The effect of blend ratio on the hysteresis energy was more evident than those of torsional rigidity and coercive torque. This was also decreased with increasing the blend ratio of polyester fiber the same as the yarn torsional rigidity. And maximum hysteresis energy loss was shown to the high level of the yarn surface helix angle. But not in the coercive torque.