To provide a composition forming a polyurethane resin excellent in heat resistance and dielectric characteristics and containing a very small chlorine quantity as impurities which may bring about corrosion of wires and poor performance of insulation resulting from wire corrosion.

The polyurethane resin-forming composition is composed of a bisphenol compound alkylene oxide addition product and diisocyanate, the former chiefly containing one mol of alkylene oxide addition product per hydroxy radical of a bisphenol compound, and yields a polyurethane resin having a glass transition temperature of 100-160 C.