The aim of this study was to examine the mediating effect of formal and informal social support on the relationship of caregiver burden and quality of life (QOL), using a sample of 320 parents (aged 50 or older) of adult children with autism spectrum disorder (ASD). Multiple linear regression and mediation analyses indicated that caregiver burden had a negative impact on QOL and that informal social support partially mediated the relationship between caregiver burden and parents' QOL. Formal social support did not mediate the relationship between caregiver burden and QOL. The findings underscored the need to support aging parents of adult children with ASD through enhancing their informal social support networks.