To provide an epoxy resin based curable composition giving a cured epoxy resin with excellent physical properties such as heat resistance and dimensional stability, etc., while keeping low water absorption, excellent dielectric characteristics.

The invention relates to the curable composition and cured articles of the same comprising (A) a compound having a heterocyclic group (a) in the molecule represented by general formula (1), (B) a compound having an epoxy group in the molecule, and (C) an active ester compound. In general formula (1), X1, Y1 and Z1 are each independently an oxygen or sulfur atom and at least one is a sulfur atom; R1 is a 2-10C hydrocarbon group.