The present invention relates to a siloxane hard resin including alicyclic epoxy siloxane alone or a reactive monomer, which is prepared by condensation reaction of alkoxysilanes, and has a weight average molecular weight in the range of 1000 to 4000 and a molecular weight distribution of PDI 1.05 to 1.4. A siloxane hard cured article produced by photo- or thermal polymerization has high hardness by compact crosslinking of siloxane molecules having different molecular weights.