Introduction: Previous studies have shown that melatonin, an anti-oxidant molecule secreted from the pineal gland, is a positive regulator of bone mass. However, the potential effects of melatonin on bone mass have never been investigated in an old population. The aim of this study was to assess the effects of dietary melatonin supplementation on mass accrual and biomechanical properties of old rat femora. Methods: Twenty 22-month-old male Wistar rats were divided into two randomly assigned groups. The first group was treated for 10 weeks with melatonin, whereas the second group was untreated (control). Rat femurs were collected, and their phenotypes and biomechanical properties were investigated by micro–computed tomography, histomorphometry, and a three-point-bending test. Statistical analyses were performed by the Student two-tailed unpaired t -test. In all experiments, a value of p <0.05 was considered significant. Results: Rats treated with melatonin had higher bone volume, bone trabecular number, trabecular thickness, and cortical thickness in comparison to the control group. Histomorphometric analyses confirmed the increase of bone volume in melatonin-treated rats. In agreement with these findings, melatonin-treated rats showed higher bone stiffness, flexural modulus, and ultimate load compared to controls. Conclusion: These compelling results are the first evidence indicating that dietary melatonin supplementation is able to exert beneficial effects against age-related bone loss in old rats, improving the microstructure and biomechanical properties of aged bones.