This observational study focuses on prosocial behaviors of children with autism spectrum disorder (ASD) during an interaction with their older, typically developing sibling (TD-Sibs). Twenty-eight sibling dyads, in which the younger sibling was diagnosed with ASD (ASD-Sibs), were video-recorded at home playing a game of their choice. Video recordings were microanalyzed, measuring frame-by-frame observational indices of prosocial behaviors. Siblings' interactions were mostly collaborative. During the interaction, the older TD-Sibs initiated more actions and the younger ASD-Sibs imitated more. The frequency of the prosocial behaviors of the ASD-Sib was associated with the frequency of the TD-Sib's prosocial behaviors. The findings emphasize the importance of sibling interactions as an opportunity for children with ASD to practice prosocial behaviors.