A series of carbosilane dendrimers uniformly functionalized with sialyl lactose moieties (Neu5Acα2→3Galβ1→4Glc) was systematically synthesized, and biological evaluations for anti-influenza virus activity using the glycodendrimers were performed. The results suggested that the glycodendrimers had unique biological activities depending on the form of their core frame, and Dumbbell(1)6-amide type glycodendrimer 7 showed particularly strong inhibitory activities against human influenza viruses [A/PR/8/34 (H1N1) and A/Aichi/2/68 (H3N2)]. The results suggested that the structure–activity relationship (SAR) on the glycolibrary against various influenza viruses was observed, and dumbbell-shaped dendrimers as supporting carbohydrate moieties were found to be the most suitable core scaffolds in this study.