X-ray diffraction and FTIR and C-13 NMR spectroscopies have been utilized to observe the inclusion compounds (ICs) formed by poly(ethylene oxide) (PEG) and low molecular weight poly(ethylene glycol) (PEG) oligomer with urea (U). We have confirmed that PEO-U-IC formed from solution has a trigonal crystal structure, while recrystallization from the melt produces a hexagonal PEO-U-IC. PEG-U-IC apparently adopts a crystal structure different from the trigonal and hexagonal forms of PEO-U-IC, and single crystals of PEG-U-IC are currently under investigation by X-ray diffraction. The conformations of PEG. and PEG chains in their U-ICs appear similar to the TGT bulk crystalline conformation, while the all-trans conformer does not appear to be consistent with either the FTIR or the C-13 NMR observations. For solution-formed PEO-U-IC in the trigonal crystal structure, where one-third of the urea molecules are hydrogen-bonded to the PEO chains and reside in the channels, the mobility of the included PEO chains is similar to that of the bulk crystalline PEG. This is quite different from the usual observations made on hexagonal polymer-U-ICs, where spin-lattice relaxation times observed for the carbon atoms of the included polymers are much reduced (often more than 1 order of magnitude) from those observed for the same polymer in their bulk crystals. It is proposed that the direct involvement of the urea molecules in the trigonal channels of PEO-U-IC with the included PEO chains is the source of their reduced mobility.