We have synthesized three different PAN copolymers with methyl acrylate (MA) and/or itaconic acid (IA) comonomers and carried out their chemical and compositional analyses. In addition, PAN and PAN/MWNT nanofibers were prepared by electrospinning PAN copolymer solutions with various MWNT contents and characterized their morphology and thermal behavior by using FE-SEM and DSC. It was found from SEM images that the PAN nanofiber with IA (2 mol%) comonomer has much smaller fiber diameter and narrower diameter distribution compared to PAN nanofibers with MA/IA (1/1 mol%) and MA (2 mol%) comonomers. For PAN/MWNT nanofibers, the fiber diameters were decreased with increasing the MWNT content. From DSC heating thermograms, it was revealed that the exothermic cyclization reactions started at lower temperatures for the PAN nanofiber with IA comonomer as well as for the PAN/MWNT nanofibers with higher MWNT contents. Overall, it was valid to conclude that the IA comonomer and the MWNT content contribute to the smaller fiber diameters and the lower temperature-initiated cyclization reactions of PAN/MWNT nanofibers which can be used as precursors for manufacturing activated carbon nanofibers.