The Eu(Ⅲ) ion, as a luminescent probe, is incorporated into a novel nanotube-contained polyorganosiloxane (POS), which is obtained by coupling of ladderlike polyvinylsilsesquioxane (Vi-T) with tetramethyldisiloxane (H-MM) via hydrosilylation, to form POS-Eu(Ⅲ) composite. The results from fluorescent study demonstrate that the composite is actually a host-guest clathrate which includes the Eu(Ⅲ) ions in the tubelike cavity of POS and moreover, the supramolecular clathrate exhibits an obvious energy transfer process which converts the UV light absorbed by POS into the visible light generated from the Eu(Ⅲ) luminescence. Molecular simulation also gives support to the formation of such a clathrate and thus results in energy transfer process.