In this research, PAN/silver nanoparticles(NPs) composite nanofibers were successfully fabricated by chemical reduction of electrospun PAN/AgNO3 nanofibers using formic acid vapor treatment. It is demonstrated that the radial compositional gradients in PAN/silver NPs nanofiber can be successfully controlled via varying treatment temperature and vapor concentration. As the vapor treatment was performed at room temperature, silver NPs were uniformly dispersed within PAN nanofiber. With increasing the vapor treatment temperature, the distribution of within vapor treated nanofiber change from well-dispersed to a core-shell structure. The morphology difference can be attributed to the temperature-dependent integrated phenomenon of formic acid vapor pressure, silver reduction rate, and mobility of silver ions within the nanofibers. Additionally, the PAN/silver NPs core-shell nanofibers can be further utilized to fabricate electrically conductive PAN/silver hybrid nanofiber mat by sintering silver NPs at the surface of the fibers. (C) 2016 Elsevier B.V. All rights reserved.