Lately, incorporation of the nano-size fillers mainly include carbon nanotubes and graphene nanosheets into the polymer electrolytes have received growing attention due to their unique mechanical, electrical, and thermal properties [1, 2]. In the present work, different weight per-cents of graphene Oxide nanosheets (GOs) [x=0.025,0.05,0.1, 0.5 wt.%] were incorporated into polyethylene oxide (PEO)/ polyacrylonitirle (PAN) nanofibrous membranes [PEO/PAN weight ratio : 75/25] via electrospinning process. Incorporation of very small amount of GOs (0.05 wt.%) enhanced ionic conductivity of PEO/PAN membranes remarkably from 3.7 mS/cm to 10.1 mS/cm. It could be due to the improved electronic conductivity of ion conducting poly-mer electrolyte and increased degree of amorphicity of the PEO matrix and thus formation of pathways for the charge carriers. On the other hand, upon adding 0.5 wt% of GO the tensile strength and Young’s modulus of the composite membrabes increased sharply by 320.6 % and 128 MPa compared with neat PEO/PAN fibrous membarne respectively. Based on the high ionic conductivity and improved mechanical properties, PEO/PAN/GO membrane could be promisingly used as a polymer electrolyte. Keywords: graphene Oxide nanosheets, polyethylene oxide, polyacrylonitirle, membranes, elec-trospinning, ionic conductivity. References: 1. Seo, S. J., Yun, SH., Woo, J. J. (2011) Preparation and characterization of quasi-solid-state electrolytes using a brominated poly(2,6-dimethyl-1,4-phenylene oxide) electrospun nanofiber mat for dye-sensitized solar cells. Electrochem. commun., 13, 1391–1394. 2. Gao, S., Zhong, J., Xue, G., Wang, B. (2014) Ion conductivity improved polyethylene oxide / lithium perchlorate electrolyte membranes modi fi ed by graphene oxide, J. Memb. Sci., 470, 316–322.