The aim of this study was to examine the experience of the first generation of sibling advocates in Hong Kong. A qualitative approach was adopted and six sibling advocates of people with intellectual disabilities from one non-government organization were interviewed. Data were analyzed using a constant comparative method and content analysis. Findings revealed that the six participants were reactive in the process of taking up the caregiver responsibility and they performed three functions: to advocate for more service provision, to improve service quality, and to facilitate communication between individual service units and family members of people with intellectual disabilities. All of the participants expressed that they needed support from service providers when they tried to function as the sibling advocates. Strategies to promote the involvement of siblings of people with intellectual disabilities as advocates are discussed and it is expected that more siblings of people with intellectual disabilities will be supported to have a higher level of involvement in advocacy.