Building construction projects have various risk factors, so accidents is easily occurred in construction field. Therefore, many studies have been carried out to find methods for reducing such accidents. However, most of these studies have been focused to engineering factors, such as working methods and safety guards and equipments. The purpose of this study is to select the key accident risk factors in building construction projects. For this study, we identified the accident risk factors, which include engineering, education, and enforcement factors, and quantitatively evaluated these factors using an analytic hierarchical process. Identifying the key accident risk factors will help to reduce accidents in building construction projects.