Hydrophobicity is considered to be a phenomenon that nonpolar solutes have a poor solubility in water? which plays fundamental roles in many chemical and biological systems. On the basis of the scaled particle theory, it has been shown in the present study that hydrophobicity is not caused by the small size of water molecules but by their high packing density generated from strong molecular interaction, Solvophobicity, observed in some organic solvents such as ethylene glycol, can be also explained consistently by the present method.