The purpose of this study was to explore the process of smoking cessation behavior in adults with a history of smoking cessation. The subjects were 17 adults selected by theoretical sampling. The data were collected by in-depth interviews using audiotape recording over a period of six months. The data were analyzed simultaneously by a constant comparative method in which new data were continuously coded in categories and properties according to Strauss and Corbin' methodology. Analysis of the data resulted in the identification of 12 categories. The result of this study are as follows : 1. Smoking cessation in adults is caused by fear about health, environmental pressure of smoking cessation, and intention of smoking cessation. 2. Smoking cessation occurs in connection with situations of limited smoking. 3. Maintenance of smoking cessation is related to psychological stress, and environmental cues to smoking. 4. In the smoking cessation process, adults experienced either health promotion or relapse. It is suggested that the result of this study may contributed to the development of a strategy for decreasing smoking behavior among adults.