By providing a composition in which refractive index can be controlled, and scratch resistivity and adhesion (especially adhesion to a resin having a thiourethane bond or epithiosulfide bond) are excellent when the composition is coated on a base material such as a resin and then cured, the composition comprises (a) a thio(meth)acrylate compound represented by the general formula (1) and (b) ultrafine inorganic particles: ##STR00001## wherein a linking(or connecting) group R represents an aliphatic residue, an aromatic residue, an alicyclic residue or a heterocyclic residue or an aliphatic residue having an oxygen atom, a sulfur atom, an aromatic ring, an aliphatic ring, or a heterocycle in the chain; R.sub.m represents each independently a hydrogen atom or a methyl group; and n is an integer of 1 to 4.