The nanomechanical properties of Kevlar(R) 49 fibers are quantitatively evaluated using the interfacial force microscope (IFM). The IFM is capable of di differentiating the skin/core structure of the fibers and selectively probing each area. The core and skin regions were found to possess an elastic modulus of 60.8 and 13.4 GPa, respectively. The difference in modulus is attributed to an increased amount of order and hence intermolecular bonding in the core region. (C) 2000 Elsevier Science Ltd. All rights reserved.