Ultrafine polyacrylonitrile/MoS2 (PM) nanofibers were fabricated by electrospinning. A homogeneous dispersion of two-dimensional (2D) MoS2 nanosheets in polymer solution is crucial to obtain a uniform distribution of nanofillers inside polymer matrices of nanofibers. Scanning electron microscopy and transmission electron microscopy images of PM revealed that the rough surface morphology resulted from the content of MoS2. X-ray diffraction analysis confirmed the reduced crystallinity of PM composite nanofibers. In contrast, the thermal properties of PM nanofibers improved, as confirmed by thermal analyses. These results indicate that the nanofiber morphology and crystallinity of PM nanofibers are significantly affected by the content of MoS2, while their thermal properties are improved by the uniform distribution of 2D nanofillers. (C) 2015 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.