In order to compare the effects of the flexible external fixations with the rigid one on fracture healing, rabbits tibiae were fractured surgically and each fracture were immobilized with external devices using graphites (the group I), plastics (the group II) and stainless steel (the group III). At six weeks after fracture, clinical and radiological union rates in group I, II and III were 91% 73% and 60% respectively. The rabbits tibiae were load in 4-point bending test to determine the mechanical properties of the fracture healing. The means and standard errors of maximum bend moment of the fractured tibiae were 11. 30±2.33kg.f. cm., 8.55±2.02kg.f. cm. and 9.79±2.09kg.f. cm. in group I, II and III respectively. These data may suggest that a certain amount of the flexibility (ex, graphite) or motion is better than the rigidity (ex, stainless steel) in fracture healing by the method of the external immobilization).