In the present study, we conducted a clinical controlled trial to evaluate the effects of cognitive behavioral therapy (CBT) training in improving depression and self-esteem in workers. A total of 261 workers were assigned to either an intervention group (n=137) or a waiting-list group (n=124). The intervention group was offered participation in a group session with CBT specialists and three e-mail sessions with occupational health care staff. Between-group differences in the change in Center for Epidemiologic Studies Depression Scale (CES-D) and Self-Esteem Scale from baseline to three months after the end of training were assessed by analysis of covariance. All subjects in the intervention group completed the group session and 114 (83%) completed the three e-mail sessions. CES-D score decreased by 2.21 points in the intervention group but increased by 0.12 points in the control group, a significant difference of -2.33 points (95% confidence interval: -3.89 to-0.77; p<0.001). The between-group difference in change of self-esteem scores was not significant. Results of the present study suggest that CBT training cooperatively provided by CBT specialists and occupational health care staff using brief e-mail is effective in improving feelings of depression in workers.