The present study examined how job demands affect an intimate partner's well-being. We hypothesized that job demands have a negative influence on partner well-being through the experience of work-family conflict (WFC) and an impaired quality of the relationship (reduced social support and increased social undermining towards the partner). METHODS: The participants of this study were 99 couples of dual-earner parents in Japan. RESULTS: Consistent with hypotheses, men's job demands (i.e. overload and emotional demands) were positively related to their own reports of WFC, and indirectly to women's ratings of men's WFC. Consequently, women's ratings of men's WFC were negatively related to the quality of the relationship (i.e. decreased social support from and increased social undermining by men), which, in turn, led to women's ill-health (i.e. depressive symptoms and physical complaints). We found similar findings for the model starting with women's job demands; gender did not affect the strength of the relationships in the model. CONCLUSIONS: These findings suggest that high job demands initiate a process of work-family conflict and poor relationship quality, which may eventually affect the intimate partner's well-being in an unfavorable way.