The present invention relates to a hydrosilation-curable organopolysiloxane resin composition comprising (A) an organopolysiloxane resin having three or more monovalent unsaturated aliphatic hydrocarbon groups and aromatic hydrocarbon carbon groups, (B) an organosilicon compound having two or more silicon-bonded hydrogen atoms and aromatic hydrocarbon groups, (C) a hydrosilation catalyst, and optionally (D) (d1) a solvent or (d2) a hydrosilation-reactive organosiloxane-based diluent, for optical transmission components, especially for optical transmission components serving as optical communication elements, relates to optical transmission components, represented by optical waveguides, comprisiong a hydrosilation-cured product of the aforementioned organopolysiloxane resin and organosilicon compound, and relates to a process for fabricatiing optical transmission components.