The purposes of this research were to investigate self-efficacy and other contributing factors in smoking cessation of smokers in the outpatient clinic at a hospital. The research subjects for this study were smokers who went to a medical center in central Taiwan for outpatient services. A structured questionnaire was used as the research tool which collected data including self-efficacy in smoking cessation, health belief, knowledge of smoking hazard, and nicotine addiction level. Through purposive sampling, each participant completed the questionnaire. 160 questionnaires were sent out beginning from March to April in 2006; 156 copies were effective and the response rate was 97.5%. The findings were summarized as follows: Smokers with better health belief, occasional smokers, smokers with lower nicotine addiction, and smokers who desired to quit smoking had higher self-efficacy in smoking cessation (r=.155, p<.05, T=8.41, p<.004, F=6.76, p<.002, T=13.92, p<.000). The results of this research can help to understand contributing factors in smoking cessation of smokers, and when combined with health promotion, this can be used for education purposes in outpatient clinic, course design of smoking cessation or group health education, and smoking-cessation counseling.