Osteoporosis is defined as a decrease in bone mass that leads to an increased risk of fracture. The therapeutic effect of 1alpha,25 dihydroxycholecalciferol, the hormonal form of vitamin D3 that mediates calcium translation in intestine and bone, on the healing process of fracture has still been controversial. These studies were designed to understand the healing process of normal fibular fracture, the osteoporotic changes after ovariectomy, and the theraqeutic effects of 1alpha,25 dihydroxycholecalciferol on the osteoporotic fracture in rats. The simple transverse fractures of rat fibulae were produced with a rotating diamond saw. The changes of the biochemical and mechanical indices of rats were investigated. The mechanical study based on bending test revealed the healing of the fibular fracture in the 5th week after simple transverse fracture. The osteoporosis impaired more the healing of osteoporotic fibular fracture than normal non-osteoporotic fibular fracture. The healing process of osteoporotic fracture was facilitated by the treatment with 1alpha,25 dihydroxycholecalciferol, however was delayed more than the healing process of normal fracture. The bone strength based on the bending test also confirmed this tendency. The bone strengths in the 5th week after fracture of normal bone, osteoporotic bone, and 1alpha,25 dihydroxycholecalciferol-treated osteoporotic bone were 75%, 41% and 67%, respectively, in comparison with those of intact bone. In conclusion, 1alpha,25 dihydroxycholecalciferol was effective in promoting the osteroporotic fracture healing.