In this paper, the polystyrene nanofiber (PSnF) with diameter in range 40-80nm were fabricated using electrospinning techniquefrom solution of polystyrene in toluene and used as an effective filler for glass fiber reinforced epoxy composite materials (GF/EP) with contents in range from 0 to 0.1 wt%. GF/EP composites with absence and presence of PSnF were characterized by different techniques, namely; mode I interlaminar fracture toughness, tensile testing and scanning electron microscope. The bonding between GF and EP were also accessed by interfacial shear strength test (IFSS). Theobtained resultsindicated that at 0.07 wt% of PSnF incorporation in epoxy matrix the stress intensity factor (K-IC), initiation and propagation interlaminar fracture toughness in mode I were improved by 42.2% from 0.631 to 0.839MPam(1/2), and 43% from 389.82 to 512.09J/m(2) and 47% from 401.38 to 545.34J/m(2), respectively, when compared to pristine epoxy resin as well as pristine composite material. The scanning electron microscopy (SEM) observation pointed out that fibers pull out during initiation delamination accounting for fracture toughness improvement the fracture surface of GF/EP.