Objectives: The Korea Health Promotion Foundation has performed the None-Smoking Project using the Quit-Smoking Clinics in all health care centers. The success rate of quitting smoking in the Quit- Smoking Clinics have run over 40% in the self-reports. The aim of this study was to assess the success rate of quitting smoking using the nicotine and cotinine concentrations in saliva and to find out the factors that influence the success of quitting smoking. Methods: The author collected the data of 122 participants from the Quit-Smoking Clinic in the city of Daejeon and the data 13 nonsmokers as control after their written consent in 2009-2010. Following the initial visit, the unstimulated saliva samples were collcted at the visits after 2 weeks, 2 months, 4 months and 6. The concentrations of nicotine, cotinine, and OH-cotinine were analyzed using the High Performance Liquid Chromatography. The cutoff for the cotinine concentration that distinguished the smokers from nonsmokers was set at 10 ng/ml. Results: The baseline participants who visited the clinic were 84 paritcipants after 2 weeks, 65 after 2 months, 40 after 4 months, and 22 after 6 months. The median concentrations of cotinine (P=0.017) and OH-cotinine (P<0.001) decreased over time. The success rates of quitting smoking were calculated at 32.1% after 2 weeks, 41.5 % after 2 months, 42.5% after 4 months, and 50.0% after 6 months, in the participants who returned to the clinic. The Cotinine level after 2 weeks correlated high-positively to the concentration of that over time (r>0.7). The amount of smoking in a day, the period of smoking, and the total amount of smoking did not correlate to the success of quitting smoking as measured in the cotinine level. Conclusions: In spite of the limitation of the high drop out rate in the participants, it was suggested that the active intervention at 2 weeks could make the success rate of quitting smoking higher, as the cotinine level at 2 weeks correlated to the concentrations after that point very positively.