Novel tetravinyl- and tetraallyl-substituted closed double-decker siloxanes (DDSQs) were synthesized and characterized, and their structures were elucidated by X-ray crystallographic analysis. Moreover, it was shown that peripheral olefins could successfully undergo hydrosilylation quantitatively. Such tetrafunctionalizable DDSQs (DDSQ-Vinyl(4) and DDSQ-Allyl(4)) thus constitute promising building blocks for more complex inorganic organic hybrid materials.