The invention discloses a novel radiation-curable silicone-based release coating composition capable of giving a cured release coating film on a substrate such as a plastic resin film exhibiting excellent adhesion to a variety of substrate materials and excellent releasability. The radiation-curable releasing silicone composition of the invention comprises (A) an aromatic compound having, in a molecule, at least two cationically polymerizable organopolysiloxanyl groups such as epoxy-substituted organopolysiloxanyl groups as the silicone ingredient and (B) a photopolymerization initiator which is an onium salt compound such as diaryliodonium salt compounds.