Background The present randomized controlled trial aimed to examine whether a newly developed psychoeducational information website on stress and depression was effective in improving depressive symptoms at one- and four-month follow-ups among workers in Japan. Methods Participants were recruited from registered members of a web survey site in Japan. Participants who fulfilled the eligibility criteria were randomly allocated to intervention or control groups. Immediately after the baseline survey, the intervention group was invited to access a psychoeducational website named the "UTSMed" within 4 months after the baseline survey. Depressive symptoms (Beck Depression Inventory II; BDI-II) were assessed as a primary outcome, at baseline, and one- and four-month follow-ups for both intervention and control groups. The analyses were conducted separately by the three subgroups (high-risk, moderate-risk, and low-risk). Results A total of 1236 workers completed the baseline survey. Participants were randomly allocated to an intervention or control group (N=618 for each), with the subgroups of high-risk (7-8%), moderate-risk (47%) and low-risk (45-46%) in each group. A significant intervention effect on improving depressive symptoms (t=-2.35, P =0.02, d=-0.57) was observed at 1-month follow-up only in the high-risk subgroup. Limitations The present study did not use a stratified permuted-block randomization. Conclusions A web-based psychoeducation approach may not be effective enough in improving depressive symptoms in a general population of workers, while it may be effective for workers who had recently sought help for mental health.