A resin composition for a PCB includes a styrene-butadiene-styrene block copolymer in an amount from 95 to 100 parts by weight, a modified porous spheres of silicon oxide in an amount from 1 to 50 parts by weight, and a liquid polybutadiene in an amount from 5 to 50 parts by weight. The styrene-butadiene-styrene block copolymer and the liquid polybutadiene both include vinyl groups on the molecular side chains. The modified porous spheres of silicon oxide also include vinyl groups. An adhesive film and a circuit board using the resin composition are also provided.