A nanofibrous membrane fabricated by electrospinning (ES) technology has found a pyramid of promising applications; to satisfy the demand of various applications, nanofibrous membranes with tunable surface chemistry are needed, and thus effective surface modification strategies for functionalizing nanofibers are highly desired. To this end, we herein report a general and convenient method to functionalize ES nanofibers. We have developed a technology that produces ES nanofibers with initiators covalently anchored on the fiber surface, which we term as iES. Subsequently, the iES nanofibers are used as a general scaffold for surface modification via surface initiated polymerization (SIP). The tunable surface chemistry, determined by application needs, was realized by the choice of specific monomers for SIP, which resulted in the desired functional polymer surface. The nanofibrous membrane modified via this method was demonstrated as the substrate for protein microarrays, showing excellent performance. Given the generality and simplicity of this method, we believe that the combination of iES and SIP will be a robust platform for extending the application of ES nanofibers.