Crystalline cyclic poly(oxyethylene)s with number-average molar masses (M-n) of 4000, 6000, and 10000 g mol(-1) were studied by wide-angle (WAXS) and small-angle (SAXS) X-ray scattering, high-frequency and low-frequency laser-Raman spectroscopy, and differential scanning calorimetry (DSC). The subcell of the crystalline cyclic polymers was the same as that of high-molar-mass poly(oxyethylene). Cyclic polymers of M-n = 4000 or 6000 g mol(-1) crystallized in their twice-folded conformation under the conditions investigated, but the cyclic polymer of M-n = 10000 g mol(-1) crystallized in a four-times-folded conformation when cooled from its melt and in a twice-folded conformation when crystallized slowly at high temperature. Comparison is made with the properties of corresponding linear poly(oxyethylene) dimethyl ethers.