Objectives: The present study was designed to identify the association between work hours and obesity in Korean adult manual and nonmanual workers, and to determine whether there is a gender difference in this association. Methods: The study was conducted using Korean National Health and Nutrition Examination Survey data collected between 2007 and 2010. Individuals aged below 25 or over 64 years, pregnant women, part-time workers, soldiers, housewives and students were excluded. The total number of individuals included in the analysis was 8,889 (5,241 male and 3,648 female subjects). The outcome variable was obesity, defined as body mass index ≥25 kg/m². Variables considered in the model were age, education, income, marital status, alcohol drinking, smoking, daily energy intake, physical activity, sleep hours per day, the type of job, work hours, and work schedule. Work hours were categorized as <40, 40-48 (reference), 49-60, and >60 hours per week. Results: In the multiple SURVEYLOGISTIC regression analyses, the adjusted odds ratio of obesity for long work hours (>60 hours per week) in male manual workers was 1.647 (95% confidence interval 1.262-2.151). Long work hours did not significantly increase the odds ratio for obesity in male nonmanual workers and female manual and nonmanual workers. Conclusions: More than 60 work hours per week increased the risk of obesity in Korean male manual workers. This result might be helpful in preventing obesity in Korean adult workers, especially male manual workers.(J Occup Health 2013; 55: 359-366)