Nafion/polyvinylidene fluoride (PVDF) nanofibrous membranes with electrostatically negative charges on the fiber surface were fabricated via electrospinning with superior water permeability and antifouling behaviors in comparison with the conventional microfiltration membranes. The fiber diameter and the resultant pore size in the nanofibrous membranes were easily controlled through tailoring the properties of the electrospinning solutions. The electrospun Nafion/PVDF nanofibrous membranes revealed high porosities (>80%) and high densities of sulfonate groups on the membrane surface, leading to praiseworthy water permeability. Unexpectedly, the water permeability was observed as proportional to the fiber diameter and pore size in the membrane. The presence of sulfonate groups on the membrane improved the antifouling performance against negatively charged oily foulants.