Hexagonally mesostructured polyoxometalate-based hybrid was prepared by a mild-solution method through the self-assembly of an amphiphilic poly(ethylene oxide) octadecyldimethylammonium (C18NEO12) and a polyanionic silicotungstic acid (HSiW). The composition of the hybrid was characterized through H-1 NMR, infrared spectroscopy, mass spectroscopy, elemental analysis, and thermogravimetric analysis, indicating an approximate formula (C18NEO12)(1.6)H-2.4(SiW12O40). The structure of the hybrid was investigated by transmission electron microscopy (TEM), scanning electron microscopy, X-ray powder diffraction, and contact angle measurement. The hybrid is a rodlike grain with the hexagonal mesostructure, which consists of one-dimensional column micelles in which alkyl chains of C18NEO12 locate at the center and poly(ethylene oxide) (PEO) part at the outside, with HSiWs anchoring at the interface, but more close to the PEO part. Furthermore, the observation of the formation process of hybrids by TEM shows that ethanol plays an important role in the self-assembly. More importantly, the hexagonal mesostructure can transform into nanofibers comprising nanofibrils in water through the disassembly.