Solution electrospinning was used for the first time to prepare nanofibers of the stable (alpha) and metastable (beta) complexes between poly(ethylene oxide) (PEO) and urea. Both types of fibers were highly crystalline and presented a large level of molecular orientation. Detailed characterization of the ill-studied beta complex was performed using wide angle X-ray diffraction (WAXD), infrared spectroscopy, and differential scanning calorimetry (DSC). Results reveal that it possesses a 3:2 PEO:urea stoichiometry and suggest that it belongs to the orthorhombic system with a = 1.907 nm, b = 0.862 nm, and c = 0.773 nm. The PEO chains are oriented along the fiber axis and present a conformation significantly affected by strong hydrogen bonding with urea when compared with the pure polymer and the stable complex. A layered structure model is suggested for the metastable complex, in which the urea molecules would be arranged into a ribbon-like structure intercalated between two PEO layers. (C) 2008 Wiley Periodicals, Inc.