Remarkably strong effects of the aromatic B3 cycle in stabilizing tubular silicon clusters were observed for the first time. The doped cluster B3@Si12+ presents a novel structural motif for silicon clusters in which a B3 cycle is encapsulated into a (6 × 2) Si12 prism giving rise to a high symmetry stable tubular structure (D3h). A large amount of electron density is transferred to the boron cycle, and the B3δ− unit not only retains a delocalized bonding pattern within the Si12 prism but also enables a two-fold aromaticity for the resulting silicon double ring. This double ring can be used as a building block to make longer nanotubes.