The invention relates to a resin composition which mainly comprises epoxy resin, a hardening accelerator, a cross-linking agent and phosphorus-containing resin, wherein the phosphorus-containing resin is bisphenol phenolic resin or phenolic resin substituted by a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide or derivatives thereof. The resin composition can be applied to semi-solidified rubber sheets or insulating layers of circuit boards. In addition, the invention relates to a semi-solidified rubber sheet, a laminating board and a circuit board containing the resin composition.