Objectives: The aim of this study was to evaluate the effectiveness of smoking cessation clinics for soldiers in the Korean armed forces. In so doing it attempted to identify the predictors of smoking cessation and positive transition of stages of change. Methods: In a single-group pre-post test study design, 5,362 smokers from Korean armed forces participated in the smoking cessation clinic programs based on both the Transtheoretical model and life skills approaches. Changes in stages of change and related variables were measured before the intervention and at 3-month follow-up after the intervention. Results: The cessation rates was 66.0% at 3-month follow-up. With the positive transition to action/maintain stage, proportion of participants in action/maintain stage increased more than 5 times after the intervention. Cons of smoking, self-efficacy, processes of change, and life skills increased, and pros of smoking decreased after the intervention. Predictors of smoking cessation included nicotine dependency, pros of smoking, high levels of self-efficacy, processes of change and life skills. Positive stage transition was predicted by pros of smoking and high self-efficacy. Conclusions: Application of the Transtheoretical model and life skills approaches provided useful strategies for a smoking cessation program in armed forces.