Objectives: The purpose of this study was to evaluate the effectiveness of a multi-component worksite stress management training (SMT) program among employees belong to Japanese steel company. Methods: Five workplaces were assigned to an intervention group and two workplaces to a control group. SMT with monthly 30-min sessions were provided to the intervention group for 6 mo. Intention- to-treat analyses were conducted among respondents of the intervention (n=96) and control groups (n=53). Results: Significant favorable intervention effects were found on knowledge (p<0.001) and marginally significant ones on professional efficacy (p=0.074) at one-month after completing the program. No significant intervention effects were observed on psychological distress, physical complaints, or job performance (p>0.05). However, in per-protocol analyses of those who attended all sessions, significant favorable effects were observed on psychological distress and job performance, as well as knowledge and professional efficacy (p<0.05). In addition, subgroup analyses revealed that those with initial low job control showed a favorable intervention effect only on knowledge (p<0.001), whereas those with initial high job control showed favorable intervention effects on knowledge (p<0.001), professional efficacy (p=0.023) and anxiety (p=0.033). Conclusions: The results suggest that the multi-component SMT program is effective at improving knowledge and professional efficacy, although job control appeared to moderate the effect of the program on professional efficacy. The program may also be effective at reducing psychological distress and increasing job performance, if participants complete all sessions.