OBJECTIVES: The present study aimed to examine the buffering effect of workplace social capital (WSC) on the association of job insecurity with psychological distress in Japanese employees. METHODS: 2,971 employees from two factories of a manufacturing company in Japan completed a self-administered questionnaire including the scales on job insecurity, WSC, psychological distress, demographic and occupational characteristics, and quantitative workload. Using psychological distress (defined as a total score of the K6 scale ≥5) as a dependent variable, multiple logistic regression analyses were conducted. In a series of analyses, interaction term of job insecurity×WSC was included in the model. RESULTS: After adjusting for demographic and occupational characteristics as well as for quantitative workload and interaction effect of quantitative workload×WSC, high job insecurity and low WSC were significantly associated with psychological distress. Furthermore, a significant interaction effect of job insecurity×WSC was observed. Specifically, the association of job insecurity with psychological distress was greater among those who perceived lower levels of WSC (prevalence odds ratio=3.79 [95% confidence interval=2.70-5.32] for high vs. low job insecurity subgroup) than among those who perceived higher levels of WSC (prevalence odds ratio=2.96 [95% confidence interval=2.19-4.01] for high vs. low job insecurity subgroup). These findings were replicated among permanent male employees in the gender-stratified analyses. CONCLUSIONS: The present study suggests that WSC has a buffering effect on the association of job insecurity with psychological distress at least among Japanese permanent male employees.