To provide an epoxy resin composition suitable for a molded product such as an optical joint part which highly requires product dimensional accuracy, and its manufacturing method.

The epoxy resin composition has a standard deviation σ of the dimension between any two pores of a molded article of ≤0.003 mm when molded as the raw material into the molded product having a length of 50 mm, a width of 10 mm, a thickness of 4 mm, a pore diameter of 3 mm, and a distance between any two pores of 30 mm. The method for manufacturing the epoxy resin composition comprises melting and kneading a mixture composed of a dry blended epoxy resin, a curing agent, a curing accelerator, and an inorganic filler by using an extruder, then pulverizing the obtained molded product to obtain a granular molding material, furthermore melting and kneading the molding material by an extruder again, and pulverizing the obtained molded product again.