Abstract Objective: This study investigated the association between functional impairments of individuals with cancer and caregiver psychological well-being, and examined the moderating effect of social support. Methods: Sixty-three caregivers (71% female) of individuals with brain tumor (n=27) and other cancers (n=36) were recruited from community services. Caregivers rated their psychological well-being on the World Health Organisation Quality of Life measure Brief version, social support on a brief version of the Social Support Questionnaire, and the individuals' functional impairments on the Patient Competency Rating Scale. Results: For caregivers of individuals with brain tumor, better psychological well-being was associated with lower functional impairment in all domains (rs=0.33-38, p<0.05), except for cognitive difficulties. For caregivers of individuals with other cancers, better psychological well-being was associated with lower functional impairment in all domains (rs=0.30-0.49, p<0.05), with the exception of activities of daily living. For the total caregiver sample, better psychological well-being was significantly correlated with overall functional impairment (r=0.34, p<0.005) and satisfaction with support (r=0.40, p<0.005). Caregivers supporting individuals with greater functional impairment had better psychological well-being if they were highly satisfied with their social support. Conclusions: Effective social support is particularly important for caregivers who support individuals with poorer functional status, and this study highlights the need to evaluate caregiver social support interventions in the context of cancer.