Purpose: The purpose of this study was to estimate the effects of lifestyle factors on metabolic syndrome (MS) among Korean adults ($age{geq}20$). Methods: A total of 7,798 subjects (weighted subjects=37,215,961) were recruited from the 2009 Fourth Korea National Health and Nutrition Examination Survey (KNHANES IV-3). Data were analyzed by t-test, ${chi}^2$-test, and logistic regression in consideration of strata, cluster and weight as national data using the SAS 9.1 program. Results: The prevalence of MS by definition of AHA/NHLBI and waist circumference cutoff points for Koreans was 22.4%. The mean clinical MS score for MS patients was 3.4, but the mean score for the non-MS group was 1.2 out of 5.0. Among the lifestyle factors, smoking (OR=1.024), stress ($0.546{leq}OR{leq}0.587$) and drinking (OR=1.005) had significant influence on the MS risk and MS scores, but exercise did not. Conclusion: The results of this study indicate that further research is necessary on the effect of lifestyle factors on MS risk and nurses should focus on effective programs about smoking, stress and drinking for the prevention and reduction of MS risk.