Introduction Mental health problems of teachers have been raised due to increased workload, violence, emotional labour in students and parents response processes. The purpose of this study is to investigate the mental health status and to find way to improve teacher’s working environment.

Methods Total 79 schools in 8 groups were randomly selected considering level(elementary, middle, academic high, vocational high) and area(urban, rural) using National Educational Statistics 2015. The questionnaire including CES-D was mailed to randomly selected schools and survey was conducted for all teachers in these schools during July to August 2016. Probable depression was defined as a CES-D score of 16 or more and definite depression was defined as a score of 25 or more.

Results 1617 out of total 3345 in 79 schools responded to the survey. Except for those who were missing information, 1123 teachers were included this analysis. Compared with the general population, teacher’s prevalence of probable depression was higher in the 30 s and 40 s (28.99% vs 22.29%, 26.46% vs 20.87%, respectively) and definite depression was higher in the 20 s, 30 s and 40 s (15.38% vs 10 0.07%, 14.01% vs 8.08%, 10.46% vs 7.57%, respectively). In the case of high school homeroom teacher, the 3rd grade homeroom teachers had a higher rate of depressive symptoms than the 1 st and 2nd grade homeroom teachers (probable depression: 39.56% vs 26.95%, definite depression 17.58% vs 11.98%).

Conclusion This study was the first to investigate the prevalence of depressive symptoms among teachers in Korea. Workers are generally known to have a lower risk of depression than the general population, but teachers have found the opposite result. The resolution of teacher’s mental health problems are almost entirely up to the individual teacher. Taking into account the impact of teacher mental health on individuals, students and schools, structural intervention is urgently needed.