A thermosetting resin composition for use with high frequencies is provided. The composition includes: (a) a polyphenylene ether having two or more unsaturated substituent groups selected from the group consisting of the vinyl group and the allyl group at both ends of the molecular chain thereof, or an oligomer of said polyphenylene ether; (b) three or more different types of cross-linking curing agents; and (c) a flame retardant. It is possible to provide a printed circuit board for use with high frequencies which simultaneously exhibits, inter alia, an outstanding low dielectric loss characteristic and good moisture-absorption heat resistance, low thermal expansion characteristics, thermal stability and outstanding working properties.