Purpose. The purpose of this study was to test the effectiveness of a comprehensive smoking cessation program for Korean adolescents. Method. The study design was quasi-experimental with one pre and three post-tests. The three posttests were done immediately after, three months later, and six months after the completion of the program. A total of 43 high school students who smoked participated in the study with 22 in the experimental group and 21 in the control group. The smoking cessation program consisted of 9 sessions with content on enhancement of self-efficacy, stress management, correction of distorted thoughts, consciousness raising, and assertiveness training. The study variables were urine cotinine levels, self-efficacy, stress, and stages of changed behavior. Results. Urine cotinine levels significantly decreased in the experimental group after the program (F=3.02, p=.06) but significantly increased in the control group (F=6.32, p=.004). Self-efficacy and the degree of stress did not change in either group. The stages of smoking cessation behavior tended to change when compared with raw data for the experimental group. For most participants, the stages of change had been precontemplation and contemplation, but changed to action and maintenance stage among the experimental group. Conclusion. The program was effective in smoking cessation and influencing stages of change but did not change psychosocial factors such as self-efficacy and stress. It is suggested a program should be developed to change psychosocial variables on a long-term basis. It is also desirable to involve peers and families of adolescents who smoke when planning programs to enhance social support.