The purpose of this study was to identify predicting factors of quitting smoking among the Royal Thai Navy Personnel. The study used a cross-sectional, descriptive correlational research design using self-reported questionnaires based on Transtheoretical model (Prochaska and DiClemente, 1983). Multi-stage random sampling was employed to obtain the sample of RTN personnel who had quit smoking for at least 24 hours in the past year. Data were analyzed using descriptive and inferential statistic of 553 RTN personnel was used to analyze the predictors. Descriptive statistics were used to evaluate characteristics health status, smoking and quitting characteristics, The alcohol use disorders identification test (AUDIT) self stress test, Fagerstrom Test for Nicotine Dependence (FTND), processes of change, decision balance, and self-efficacy. Logistic regression analysis was used to calculate odds ratios with 95% confidence interval of abstinence rates for each variable. And the level of any statistical tests was established at p = 0.05 The results indicated that the predicting factors of quitting smoking among the Royal Thai Navy were length of past quit attempt (OR=1.05, 95% CI=1.04-1.06), family support (OR=1.51, 95% CI=1.06-2.15), conscious raising (OR=1.5, 95% CI =1.06-2.15), social liberation (OR=.81, 95% CI=.73-.90), self-reevaluation (OR=.84, 95% CI=.0.75-0.94),counter condition (OR=1.15, 95% CI=1.03-1.29). The best equation of logistic regression explained to 56.5% of the variance in quitting smoking among the RTN personnel.