The invention can provide a high-refractive-index resin composition containing particles, more particularly, a resin composition having a high refractive index and usable in optical applications including coatings and lenses. The high-refractive-index resin composition of the invention is a high-refractive-index resin composition obtained by polymerizing a polymerizable composition containing particles coated with a surface-treating agent and having an average particle diameter of 10 nm or smaller and a polymerizable monomer, wherein the content of the particles excluding the surface-treating agent, X (% by mass), and the refractive index of the high-refractive-index resin composition, Y (n.sup.23d), have a relationship between these which is represented by the general formula 1: Y.gtoreq.0.0035X+1.52 (wherein 20.ltoreq.X.ltoreq.60 and Y.ltoreq.2.0).