Bone defects are very challenging in orthopedic practice due to a variety of reasons. Bone repair requires four critical elements, biocompatibility, osteoconduction, osteoinduction and osteogenesis. The autografts still exist some problems for applications such as the limitation of available autogenous bones and post-operative complications, although they are considered as the “gold standard” in bony defect repairs. Generally the synthetic bone substitutes do not possess osteoinductive and osteogenic activities. Therefore, the clinical bone grafts and bone-graft substitutes have their own shortcomings in the repair of bone defects. Biodegradable magnesium-based metals, including pure magnesium and magnesium alloys, have been concerned and studied recently due to their biodegradation, good biocompatibility and similar elastic modulus and density with bone tissue. This paper summarizes the biological behavior of magnesium-based metals for bone defects repair application, including ability of promoting osteogenesis, osteoconduction and potential osteoinduction, as well as some particular biofunctions such as antibacterial and antitumor properties. The great advantages and potentials of magnesium in bone defects repair can not be denied as a promising class of bone substitutes, although further researches are still needed for clinical applications.