OBJECTIVE: Prostate cancer (PCa) is an external stressor that can affect both patients and partners, but dyadic research in this area is limited. This study, guided by the vulnerability-stress-adaptation model, examines how PCa distress affects relationship satisfaction through psychological flexibility and self-esteem. METHODS: The study used a cross-sectional design with a total sample size of 314 dyads. The actor-partner interdependence model was applied to examine both actor and partner effects. Covariates were also examined. RESULTS: PCa distress negatively predicted psychological flexibility in both patients ( CONCLUSION: The findings highlight the critical role of psychological flexibility and self-esteem in mediating the impact of PCa distress on relationship satisfaction for both patients and partners. Tailored interventions aimed at enhancing psychological flexibility to support relationship functioning in couples coping with PCa may be effective.