The polarized infrared spectra of water in the middle phase of Triton X100 aqueous solution were compared with those of poly(ethylene oxide) in the crystalline state, The oxyethylene chain of TX100 orients approximately perpendicular to the direction of the stream (parallel to the direction of growth of the liquid crystal), while that of poly(ethylene oxide) orients parallel to the stretching direction, However, in both cases the water molecule prefers the perpendicular orientation of its bisector to the oxyethylene chain, The OH stretching frequency of water in Triton X100 sharply increases with increasing water content up to about 10 wt% and decreases suddenly up to about 40 wt% after which it stays constant, The initial increment in the OH stretching frequency is due to the progression of the hydrogen bonding between water and the ether oxygen in the oxyethylene groups of Triton X100 and the subsequent reduction is the result of the linkage between the waters, On the other hand, the increase in intensity and the decrease in band-width of the 949 cm(-1) band up to a constant value at about 40 wt% H2O suggest the progression of the ordered GTTG helical conformation in the oxyethylene group of Triton X100, The appearance of the middle phase of Triton X100 results in the formation of the hydrogen-bonding network of the (2:1) complex at about 40 wt% H2O. In the middle phase of 40-60 wt% H2O, water added in excess gradually dissolves the linkage among the adjacent oxyethylene chains, but the system partially remains in the liquid crystal phase. Above 60 wt% H2O (water:oxyethylene = 5:1), the water added in excess interrupts the hydrogen-bond linkage of the 2:1 complex and destroys the middle phase. However, the helical conformation resides in this aqueous solution, because the oxyethylene group prefers the helical conformation in the aqueous solution rather than in the neat or molten state, The C-13 chemical shifts ensured the concurrence of hydration to the various oxygen atoms in the oxyethylene chain and the existence of the helical conformation. In the middle phase, the weak orientation of water and TX100 is due to the directional distributions of the helical axis in the quasi-spherical micelle.