The invention relates to a resin composition used for forming a dielectric layer of a dielectric substrate for an antenna. The resin composition comprises (A), epoxy resin containing a naphthalene nucleus or diphenyl structure, (B), any one of or a mixture of at least two of tri(4-hydroxyphenyl) methane type epoxy resin, o-cresol type novolac epoxy resin and phenol type novolac epoxy resin, (C), a resin fusion viscosity modifier, and (D), spherical ceramic powder after presintering treatment. With the adoption of the resin composition, the obtained dielectric substrate has a high dielectric constant, high peeling strength, a low thermal expansion coefficient and very good thickness consistency, and can meet a performance requirement of the high dielectric constant antenna substrate.