The present study aims to investigate the mediating effect of dispositional coping on the relationship between cognitive appraisal (which includes areas of threat, challenge, harm/loss, and benign/irrelevant appraisals) and posttraumatic growth (PTG) among patient–caregiver dyads undergoing hemodialysis. In total, 237 dyads of patients undergoing hemodialysis and their family caregivers were recruited from a tertiary hospital in Tianjin, China. Dyadic data were analyzed using the Actor–Partner Interdependence Mediation Model (APIMeM). The final APIMeM model examining dyadic effects of challenge appraisal and dispositional coping on PTG demonstrated an excellent model fit. The challenge appraisal of family caregivers was directly associated with the PTG of patients undergoing hemodialysis. Dispositional coping mediated the pathways between challenge appraisal and PTG for both patients undergoing hemodialysis and family caregivers. By exploring the cognitive appraisal and dispositional coping of patient–caregiver dyads undergoing hemodialysis may help both partners foster PTG.