To provide a phyllosilicate dispersed into a dispersive medium such as a synthetic resin, and improving the oxidation resistance of the dispersive medium, to provide a hardenable composition reacted with moisture or the like in the air so as to be hardened, capable of obtaining a hardened material excellent in oxidation resistance and weather resistance and suitably used for sealing materials, adhesives or the like, and to provide a sealing material and an adhesive consisting of the hardenable composition.

The phyllosilicate is obtained by being modified with a compound containing a functional group having oxidation prevention effect. The hardenable composition is obtained by dispersing the phyllosilicate into an organic polymer containing at least one hydrolyzable silyl group capable of crosslinking. The sealing material comprises the hardenable composition. The adhesive comprises the hardenable composition.