Background: Most smokers in developing countries begin smoking before age 18, and smoking prevalence is rising among adolescents. School personnel represent a target group for tobacco-control efforts because they interact daily with students, are role models for students, teach about tobacco-use prevention in school curricula, and implement school tobacco-control policies. The prevalence of teenage smoking has been examined in numerous studies, but few have focused on the influence of school personnel and the characteristics of school personnel who enforce school nonsmoking policy. The purpose of this study was to determine the factors associated with junior high school personnel advising students to quit smoking. Methods: School personnel (N = 7129) were recruited by cluster sampling from 60 junior high schools in Taiwan; of these, 5280 voluntarily returned self-administered, anonymous questionnaires (response rate = 74.06%) in 2004. Results: Most personnel (70%) had advised students to quit smoking. School personnel who were older, male, responsible for teaching health, smokers, with positive attitude against tobacco, or with more knowledge of tobacco hazards were more likely to advise students to quit smoking. Personnel with more interest in and access to tobacco-related materials were more likely to advise students to quit smoking. Personnel who had received tobacco-prevention training were 2.41 times more likely to persuade students to quit smoking after adjusting for other factors. However, only half of the participants had ever had access to educational materials about tobacco use, and 8% had ever received training to prevent tobacco use. Conclusions: To reduce youth smoking prevalence, school tobacco-control programs should support tobacco-prevention training for school personnel. (Contains 5 tables.)