The authors investigated methodologically the mechanical characteristics of the callus in the healing of human long bone fractures. We proposed utilizing the statistical data from the fibular callus of the rabbit in the literatures for the estimation of the yield stress of the human callus. A three-dimensional finite element model was established for the fractured human long bone the gap of which was filled with callus. We observed the followings;1. With the increasing strength of the callus, progressive decrease in stresses was observed at the cortical surface and cancellous portion, while progressive increase in stresses at the callus portion. 2. Stresses observed at the callus were greater on torsional load when the strength of the callus was low, while those were greater on bending loads when the callus strenght was high. 3. The yield load of the callus was higher than any other portion of the long bone in the latest stage of the healing.