The novelty of this work is based on designing the chemistry of the electrospun nanofibers, so that the resultant composites substantially benefit from cross-linking between the nanofibers and the polymer matrix. Specifically, the solution of in-house synthesized copolymers polystyrene-co-glycidyl methacrylate P(St-co-GMA) is electrospun to produce mats of surface reactive nano-to-submicron scale fibers that are accompanied later by spraying over the ethylenediamine (EDA) as a supplementary cross-linking agent for epoxy. The P(St-co-GMA)/EDA fiber mats are then embedded into an epoxy resin. Analysis of the three-point-bending mode of the composites reveals that the storage modulus of P(St-co-GMA)/EDA nanofiber-reinforced epoxy are about 10 and 2.5 times higher than that of neat and P(St-co-GMA) nanofiber-reinforced epoxy, respectively, even though the weight fraction of the nanofibers was as low as 2 wt %. The significant increase in the mechanical response is attributed to the inherently cross-linked fiber structure and the surface modification/chemistry of the electrospun fibers, that results in cross-linked polymer matrix−nanofiber interfacial bonding.