Abstract: The present invention relates to a photopolymerizable composition; more specifically, the present invention relates to a photopolymerizable composition useful as photoimageable solder mask of one component type, which can form image by ultraviolet exposure and development in an aqueous solution of dilute alkali after film formation and which has excellent ultraviolet curability and heat resistance of solder. The composition contains a reaction product, a diluent and a sensitizer, the reaction product being produced by adding epoxy group-containing acrylic acid ester or epoxy group-containing methacrylic acid ester to a part of the carboxyl group of the copolymer of acrylic acid ester or methacrylic acid ester with acrylic acid or methacrylic acid.