A nonaqueous gel composition for tooth whitening, comprising: (A) tooth whitening ingredient having a relative permittivity of 17.0 to 43.0 (at 25.degree. C.) and a vapor pressure of 0 to 7000 kPa (at 25.degree. C.), (B) substance that is soluble in the tooth whitening ingredient and is precipitated by an aqueous solution of calcium chloride, and (C) gelling agent, which nonaqueous gel composition contains substantially none of water and peroxide. This tooth whitening component can penetrate into the enamel surface layer of teeth to thereby alter the optical properties, such as refractive index and reflectance, of the enamel so that the enamel is apparently whitened. The whitened teeth can be restored to the original tooth color in a reversible manner in the presence of water. Further the persistence of reversible whitening effect can be strikingly enhanced by the nonaqueous gel composition.