Purpose: This study identified and compared influential variables on intention and action to quit smoking between adolescent smokers and adult smokers. Methods: For the selection of variables, the transtheoretical theory was used. A survey was conducted with 376 adolescent smokers in 4 high schools and 451 adult smokers in community settings in South Korea. Discriminant analysis was used for data analysis Results: The variables of adolescent smokers that predicted an intention to quit smoking were: smoking temptation, self re-evaluation, counter conditioning and stimulus control. The variables that predicted an action to quit smoking were: self-efficacy for smoking abstinence, pros for smoking, self reevaluation, and self liberation. The variables of adult smokers that predicted an intention to quit were: smoking temptation, pros for smoking, cons for smoking, self reevaluation. The variables that self liberation and predicted an action to quit smoking were: self efficacy for smoking abstinence, smoking temptation, and counter conditioning. Conclusions: Developing stage specific smoking intervention methods based on different ways of how individuals make a decision to quit smoking within their contexts needs to be done.