Abstract: In order to study the molecular interactions involved in dilute ethanol-water solutions, the OH stretching vibration spectra of ethanol-water solutions with the concentration range of 0-10 vol.% were measured, and the difference spectra of the samples were calculated. The hydration of ethanol molecule in the solutions of low concentration was analyzed based on the difference spectra. The result shows a very small amount of ethanol in the solution can enlarge the hydrogen bonding network in pure water, and the hydrogen bonding degree of water molecules around hydrophobic groups of ethanol molecules was also enforced. Ethanol molecules tend to aggregate together with increasing concentration, which was caused by hydrophobic hydration, and the hydrogen bonding network of water molecules become loosen due to this. As a result, some of the water molecules break away from the hydrogen bonding network, and transfer to small clusters of different size; at the same time, the hydrophilic groups of ethanol molecules associate with free water molecules through hydrogen bond.