The low-frequency Raman spectra of dioxane aqueous solutions have been analyzed from a dynamical aspect of water structure. The reduced Raman spectra chi"(<(nu)over bar>) of the dioxane aqueous solutions are well explained by a superposition of three characteristic modes of water and one Gaussian mode (similar to 60 cm(-1)) of dioxane. The concentration dependence of chi"(<(nu)over bar>) spectra shows that the 190 cm(-1) mode of water disappears below about 0.8 molar fraction of water, This molar fraction corresponds to the ratio of four water molecules to one dioxane molecule. This means that the tetrahedral-like structure of water which is formed by five water molecules is almost destroyed below about 0.8 molar fraction. Thus the basic idea of the five water molecules model of liquid water has been confirmed from Raman spectroscopic point of view.