Past research indicated that long working hours may increase the risk of depression, especially when working for more than 40 hours. This study explores the relationship between the number of work hours and depression among high school, junior high school, and elementary school teachers. The mediating role of subjective well-being was also examined. Nine hundred and eighty four teachers were randomly selected from the north, central, and south regions of Taiwan. All participants completed two questionnaires-the Subjective Well-Being Scale and Taiwan Depression Scale-for assessment of subjective well-being and depression. Results show that teachers with longer working hours have higher risk of depression. Second, there were significant differences in the number of work hours among the three groups of teachers. Third, subjective well-being mediated work hours and depression among high school teachers. Finally, suggestions for practice and future research are proposed.