It has been reported that low-intensity laser treatment has many biological effects and the acceleration of bone regeneration by laser has been the focus of contemporary research as it may hold great potential benefit for clinical therapy in orthopedics and dentistry. However, biological effects of laser irradiation on bone are not fully elucidated. We have been investigating the effects of laser irradiation on bone formation and tooth movement, and the stimulatory mechanisms involved by in vivo and in vitro experiments. These results will be presented and the possibility of clinical laser application in orthodontics will be also discussed.