In this work, electrospinning was carried out using 12 wt.% poly(ethylene oxide) (PEO) solution under fixed tip-to-collect distance (10 cm) and voltage (15 kV) in order to fabricate nanofibers-reinforced composites. The content of PEO nanofibers was varied from 0 to 10 wt.% in the epoxy (EP) matrix resins. And the PEO powders-impregnated composites were also prepared to compare with physicochemecal properties of nanofibers-reinforced composites. Thermal and mechanical interfacial properties of EP/PEO nanocomposites were characterized by thermogravimetric analysis (TGA) and fracture toughness test, respectively. As a result, the PEO-based nanofibers-reinforced composites showed an improvement of thermal stability parameters (initial decomposed temperature (IDT) and integral procedural decomposition temperature (IPDT)) and fracture toughness factors (KIC and GIC), compared to the composites impregnated with PEO powders. And the thermal and mechanical interfacial properties of the composites were increased with increasing the PEO content, which could be probably attributed to the higher specific surface area and larger aspect ratio of PEO nanofibers, resulting in improving the demand performance of the nanocomposites.