An photo-curable sealing agent composition comprising (A) an unsaturated group-containing urethane resin having a number average molecular weight of 1,000-100,000 and an unsaturation degree of 0.1-1 mol/kg, which is obtained by reaction of (a) a polycarbonate diol having a number average molecular weight of 500-3,000, (b) a bifunctional epoxy (meth)acrylate having two hydroxyl groups and two ethylenically unsaturated groups, and (c) a polyisocyanate; (B) a (meth)acrylic acid ester monomer, wherein an alcohol residue, ester-bonded with an (meth)acyloyl group, is a hydrocarbon group which may contain an oxygen atom, and has 1-20 carbon atoms and a molecular weight of not larger than 1,000; and (C) a photo-polymerization initiator. The sealing agent composition exhibits a high curability performance and gives a cured product having a low hardness and enhanced flexibility and elongation, and improved physical and mechanical strength and enhanced durability.