To provide a refractive index pattern and an optical material whose refractive indices are changed by a simple method, which have a sufficiently large refractive index difference and which are stable irrespective of their use conditions, and a method of forming these.A radiation sensitive refractive index changing composition comprising (A) a decomposable compound, (B) a hydrolyzate of an alkoxide such as tetrabutoxytitanium, tetramethoxyzirconium, tetramethoxygermanium or tetramethoxysilane, or a halogen compound such as tetrachlorosilane and (C) a radiation sensitive decomposer; and a method of producing a refractive index pattern and an optical material, using the above radiation sensitive refractive index changing composition.