A method for fabricating a substrate structure is provided, which includes the steps of: disposing at least a strengthening member on a carrier; sequentially forming a first circuit layer and a dielectric layer on the carrier, wherein the strengthening member is embedded in the dielectric layer; forming a second circuit layer on the dielectric layer; removing the carrier; and forming an insulating layer on the first circuit layer and the second circuit layer. The strengthening member facilitates to reduce thermal warping of the substrate structure.