Patients who have multiple chronic conditions (MCCs) and their informal caregivers experience poorer health-related quality of life (HRQOL). Perceived social support has been shown to influence HRQOL. This study aimed at identifying the differences between patients' and caregivers' physical and mental HRQOL; and determining the association between their perception of social support from different sources, and their own and their dyad partner's HRQOL. Patients with MCCs and their caregivers (345 dyads) were enrolled in a multicenter cross-sectional study conducted in Italy. The Multidimensional Scale of Perceived Social Support measured perceived social support from family, friends, and significant others, and the 12-Item Short-Form Health Survey measured the physical and mental component of HRQOL in dyads. The dyadic analysis was conducted using the Actor-Partner Interdependence Model through structural equation modelling. Family support perceived by each member of the dyad was associated positively with their own mental HRQOL, and that family support perceived by caregivers was also associated positively with patients' mental HRQOL. Greater family support perceived by caregivers was also associated with better physical HRQOL in both caregivers and patients. Moreover, greater friend-support perceived by each member of the dyad was positively associated with own physical HRQOL. The study suggests the reciprocal influence of perceived social support from family and friends on physical and mental HRQOL in MCC dyads. Healthcare professionals should identify those people who are the main sources of support for each member of the dyad, and develop care plans that promote the maintenance and enhancing of this support. Copyright © 2020 Elsevier Ltd. All rights reserved.