A circuit board includes an insulating made by a low dielectric resin composition includes a low dielectric resin containing acid anhydride, an epoxy resin, polyphenylene ether resin with vinyl and active esters, maleic acid liquid polybutadiene, and an accelerator. Such low dielectric resin can be dissolved in organic solvent more easily than a low dielectric resin without acid anhydride, and the low dielectric resin containing acid anhydride has a better compatibility with other organic components than a low dielectric resin without acid anhydride. A low dielectric resin composition with lower dielectric constant and better properties can thus be obtained.