Object of the present invention is to provide a preparation for oral cavity that is appropriately usable as a prophylactic agent for dental caries, a therapeutic agent for dental caries at early stage, a prophylactic and/or therapeutic agent for dentinal hypersensitivity, a preparation for the lining of a dentin cavity surface, or the like, which has a superior effect of sealing the dentinal tubules, is capable of improving the acid resistance of the teeth and re-calcifying the teeth, ensures a short-time treatment with an easy operation, and has a high safety and good aesthetic properties. The object is achieved by a preparation for oral cavity such as a prophylactic agent for dental caries and/or a therapeutic agent for dental caries at early stage, a prophylactic and/or therapeutic agent for dentinal hypersensitivity, a preparation for the lining of a dentin cavity surface, or the like, consisting of a liquid (A), in which fluoro-alumino-silicate glass microparticles are dispersed, and an aqueous inorganic phosphoric acid solution (B).