A highly ordered, porous nanoscale network structure of polyoxomolybdate was prepared from the slow decomposition of an unstable precursor compound MoO2(OH)(OOH) in the presence of PEO-containing triblock copolymer gels or sernidilute/concentrated poly(ethylene oxide) (PEO) homopolymer solutions. Small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) measurements of the 1-mum size crystals revealed an extremely ordered primitive cubic (pc) structure made of polyoxomolybdates. Scanning electron microscopy (SEM) measurements showed that the overall size of these single crystals was close to 1 mum, in agreement with estimates from the scattering peak widths. Evidence from both scattering measurements and transmission electron microscope (TEM) measurements suggested that the system formed a highly porous primitive cubic network similar to that of certain zeolite structures. However, the observed lattice constant of 5 nm was much larger. The function of the PEO-containing polymer network was found to be very subtle and complex. Presumably, PEO acted simultaneously as a weak reducing agent and as a viscous matrix to ensure sufficient time for the formation of long-range ordered structures, resulting in the growth of extremely uniform but probably hollow "nanospheres". We suggest that this new material may find unique applications as a high-efficiency absorbent or catalyst. Furthermore, the current synthetic method may open up new pathways to prepare similar functional nanomaterials.