For the purpose of clarifying the fracture healing process from a rheological standpoint, the author attempted to study the change in physical characteristics of the callus. The study was conducted as follows: a cortical defect without fracture was made in the tibia of a mature rabbit, and a dynamic viscoelasticity test and static tensile test were made. A two-dimensional finite element model of the fracture area of the long bone was developed to simulate changes in the strength. Thus, the difference in the strength of the fracture area with and without internal fixation was compared and studied. As results, 80% of the strength was gained within 12 weeks in both the dynamic viscoelasticity test and the static tensile test. It also became clear that the bending strength of non-fixation group with an abundant external callus exceeded that of the internal fixation extraction group in the simulation test.