To investigate the effect of 25-OH-vitamin D supplements (calcidiol) on fracture healing in the elderly, an experimental model with 15 18-month-old female Wistar rats was designed. An experimental fracture in the middle third of both femora of each rat was made. Then the rats were randomly assigned to two groups: one group was subcutaneously treated with 25-OH-vitamin D during all healing processes, and the other group (the control group) was not. After 5 weeks of healing, the animals were killed and both femora were extracted. Blood samples were collected before fracture and at death to determine the levels of 25-OH-vitamin D. All bones that were extracted were subjected to a torsion test to assess healing; a significantly greater maximum shear force before failure was supported in the treated group (p < 0.01). Moreover, a positive correlation (p < 0.01; r=0.55) was found between blood levels of 25-OH-vitamin D at death and the mechanical strength of the callus. Thus, the administration of 25-OH-vitamin D after the experimental fracture significantly improved the mechanical strength of the fractured bone. If similar results are found in the human, then treatment with 25-OH-vitamin D after the occurrence of a fracture would be a good way to improve fracture healing in the elderly.