This study was performed with the questionnaire survey on mercury knowledge and mercury exposure avoidance behavior, which was conducted among 1076 dental personnel in September, 2004. As for the factors effecting the mercury knowledge, it seems that they are closely related with the personnel’s educational backgrounds, and their understandings of causing environmental hazardousness in the dental offices. And also, the factors effecting the behavior of mercury exposure avoidance are strongly connected with the knowledge points on mercury, the knowledge of air states in the dental clinic offices, the use of pincettes and gloves in squeezing, and rubber dam and gloves in mulling, the experience of environmental education on mercury, etc. In the survey, the higher points in mercury knowledge is closely related with the higher points in the behavior of mercury exposure avoidance. Nevertheless, the very fact that the lower points in the behavior among personnel takes on the aspect of the relatively higher points in knowledge on mercury may be understood that the generally acquired knowledge on mercury cannot be the critical factor of the behavior of mercury exposure avoidance.