Objectives: The purpose of this study was to identify the associations between the reasons of Korean adolescents' attempts for quitting smoking and their conventional-electronic cigarette use experience. Methods: This research was based on mixed methodology. Data from the 2014 Korean Youth Risk Behavior Web-based Survey (KYRBWS) of 72,060 students aged 13-18 years were analyzed with logistic regression. In-depth Intimate interviews were performed with 11 male high school student smokers who had e-cigarette experience and analyzed by using Colaizzi’s method. Results: Conventional cigarette only users were 3,783 (5.4%). 77% of e-cigarette users were dual users. Among ever smokers, those who have smoking friends (OR 6.7; 95% CI 4.0-11.2) and have smoking amount ≥20 cigarettes per day (OR 3.9; 95% CI 2.7-5.6) were more likely to be dual users. In the interview, the students had purchased e-cigarette to save money by quitting smoking on the increase in cigarette prices. Influence from peers and convenience (i.e. the absence of odor) was other reasons for using e-cigarette. They became dual users because not satisfied with e-cigarette. The internet was an important distribution channel for e-cigarette. Conclusions: E-cigarette users became dual users because it was not satisfactory. Further research should be followed to regulate the spread out of e-cigarette in adolescents.