The purpose of this study is to discover the key factors to prevent unsafe behavior of a construction worker. Industrial accident statistics in 2013 show that the mortality of construction workers is highest and Heinrich said that most of the accidents caused by unsafe behavior. Installation of safety facilities and safety training in construction sites have improved a lot compared to the past but disaster caused by the unsafe behavior of workers are still occurring at the construction sites in all over the country. This study attempts to investigate the causes and present countermeasure of unsafe behaviors of construction workers. It showed that self management, personal nature of the workers, relief of stress, improvement of work environment are needed most in order to avoid unsafe behavior thorough this study. The output throughout this study are as follows the first securement of optimal construction period, the second education and observation about workers in their fourties and unskilled workers, the third improvement of working environment, the fourth, obey of safety rule, the fifth, drastic safety inspection, the sixth stress relief of workers, the seventh self-control safety management. Based on these findings I anticipate that this study will become a practical guideline to prevent unsafe behavior of domestic construction workers and experimental research for proving effectiveness of the guidelines is done and to be foundation to eradicate unsafe behavior in the construction industry.