Objectives: The purpose of this study is to analyze factors associated with depression among workers in South Korea by socio-economic factors, health behaviors, and working conditions. Methods: Study subjects include 4,251 adults (19 and older) who are currently working using the data from 2009 National Health and Nutrition Survey. Data were analyzed using frequency test, $X^2$ test, and multiple logistic regression. Results: Multiple logistic regression analysis showed that gender (OR=1.91, p<.001), age (OR=1.53, p=.030), marital status (31-39: OR=1.88, p=.029) were significantly related to depressing among socio-economic factors. Next, among health behaviors factors, perceived health status (Poor: OR=1.76, p=.049; Very poor: OR=3.46, p=.002) was statistically significant. Among characteristics of work environment, trust and respect (OR=1.34, p=.049) and working with hidden emotion (OR=1.88, p<.001) were significantly related to depression. Conclusions: In order to manage and reduce depression among workers, it is important to develop appropriate mental health promotion programs both in work places and in regulations.