The development of novel nanomaterials with well-controlled morphologies/structures to achieve excellent activities/sensitivities in surface-enhanced Raman scattering (SERS) is crucial in advancing the high-performance SERS detections of chemical and biological species. In this study, amidoxime surface-functionalized polyacrylonitrile (ASFPAN) nanofibrous membranes surface-decorated with silver nanoparticles (Ag NPs) were prepared via the technique of electrospinning followed by the method of seed-mediated electroless plating. High SERS activities/sensitivities were observed from the ASFPAN-Ag NPs nanofibrous membranes, while the density and size of Ag NPs had an important impact on the SERS activity/sensitivity. The results confirmed that the enhancement of Raman signals is due to the presence of hot spots between/among Ag NPs on the nanofiber surfaces. Electrospun nanofibrous membranes surface-decorated with Ag NPs were mechanical flexible/resilient and could be used as highly active/sensitive SERS substrates for a broad range of applications.