This study investigated the initial evidence of internal structure and convergent validity of the Brazilian version of the Medical Outcomes Study Social Support Survey (MOS-SSS) in caregivers of individuals with intellectual disabilities. This study included 185 caregivers of individuals with disabilities who were users of a non-governmental organization in southeastern Brazil. We performed exploratory and confirmatory factor analyses, internal consistency reliability, and predictive validity analyses. Our results demonstrated a one-dimensional internal structure for the adapted scale, consisting of nineteen items and presenting good precision coefficients (α = 0.96 and ω = 0.96) and composite reliability (0.96). Also, the MOS-SSS showed convergent validity with the Family APGAR Scale and the family support and self-control factors of the Informal Caregiver Burden Assessment Questionnaire-Short Version. These findings suggest that the Brazilian version of the MOS-SSS has adequate psychometric properties and can be used in this context and population.