To provide a resin composition with an excellent dielectric property, a dimensional stability and a mounting reliability, a resin layer and a carrier material with the resin layer, and a circuit board.

The resin composition includes (A) a cyclic olefin resin and (B) one or a plurality combinations of a porous inorganic filler, an inorganic hollow filler, polytetrafluoroethylene (PTFE) particles, wherein the cyclic olefin resin preferably includes a polynorbornene resin.