Purpose: The purpose of this study was to identify factors affecting on the successful cessation of smoking for six months in the smoking cessation clinic of a public health center. Methods: The subjects of this study were 568 adult smokers who had registered in the smoking cessation clinic of a public health center in B City. Data were analyzed through $x^2$-test, t-test, and logistic regression using the SPSS/WIN 12.0 program. Results: Identified factors affecting the successful cessation of smoking for six months were service type, number of counseling, alcohol problem, previous quit-smoking trial, dependency on nicotine, CO level in expiration at the first visit time, self-reevaluation, helping relationship, negative/affective situational temptation, and Cons. Conclusion: Trans-theoretical Model variables were confirmed as factors affecting the success of smoking cessation. Based on the results of this study, a smoking cessation program was suggested, which uses Trans-theoretical Model variables affecting smoking cessation for six months in a public health center.