Different from conventional nonionic poly(oxyethylene) surfactants, poly(oxyethylene) cholesteryl ethers, ChEO(n), possess a bulky and nonflexible hydrophobic part and form a variety of self-organized structures in water. We investigated the phase behavior and the micellar structures in the water/ChEO(15) and water/ChEO(10) systems by means of visual observation, rheometry, small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), dielectric relaxation spectroscopy (DRS), and densimetry. We found that in the water/ ChEO(15) system, aqueous micellar (W-m), discontinuous micellar cubic (I-1) with Fd3m space group, hexagonal (H-1), rectangular ribbon (R-1), and lamellar (L-alpha) phases are formed, whereas W-m, unknown, R-1, defected lamellar (L-alpha(H)), and L-alpha phases are produced in the water/ChEO(10) system at ambient temperatures. Compared with a conventional aqueous nonionic surfactant system, the intermediate R-1 phase region is incredibly wide. As for the water/ChEO(15) system, with increasing water content, the packing parameter, P, in the R-1 region is gradually decreased, finally converging to 1/2 at W-s similar to 0.58, indicative of the formation of the H-1 phase. The R-1 phase acts as a "distorted" hexagonal phase in the system. However, in the water/ChEO(10) system, upon reduction of W-S, P shows a steplike increase and the maximum value similar to0.67 at W-S similar to 0.7, just corresponding to the threshold of discontinuous and bicontinuous structures. After that, P is decreased with decreasing Ws and unknown phase that cannot be indexed to any known space group for liquid crystalline phases emerges at W-S similar to 0.5. The GIFT analysis of the SAXS data for the W-m solution indicates that spherical micelles are present in the water/ChEO15 system in an ambient temperature range, but ChEO(10) forms a short-rod micelle in water. With increasing temperature, rodlike micelles appear to be grown and a viscoelastic micellar phase is formed in water/ChEO10 system. The hydration number for each oxyethylene unit is evaluated as similar to4 by DRS, which gives a consistent explanation for the concentration dependence of the apparent hydrodynamic radius in the Wm phase obtained by DLS. Hydrated water molecules should be regarded as a constituent of the micelles. The majority of these features of novel phase behavior in the water/ChEO(n) systems are based on a nonflexible and bulky hydrophobic part of ChEO(n).