By choosing V-shaped ligands, Cu2+ cations and isopolymolybdates as starting materials, a novel double helical compound [Cu(H2O)(bimb)]2[β-Mo8O26] (1) (bimb = 1,3-bis(1-imidazoly)benzene) was hydrothermally synthesized and characterized by elemental analyses, single-crystal X-ray diffraction, powder X-ray diffraction and IR spectroscopy. A structural feature is that compound 1 represents the first example of a helical compound based on polyoxometalates, which possesses an unprecedented helical disposition, namely the coexistence of both interconnected and interweaved double helices in one structure. The photocatalytic properties of compound 1 were also investigated in detail and the result of photocatalytic experiments shows that compound 1 can be used as a stable photocatalyst toward the decomposition of the organic pollutant methylene blue.