Demyelination of the myelinated peripheral or central axon is a common pathophysiological step in the clinical manifestation of several human diseases of the peripheral and the central nervous system such as the majority of Charcot-Marie-Tooth syndromes and multiple sclerosis, respectively. The structural degradation of the axon insulating myelin sheath has profound consequences for ionic conduction and nerve function in general, but also affects the micromechanical properties of the nerve fiber. We have for the first time investigated mechanical properties of rehydrated, isolated peripheral nerve fibers from mouse using atomic force microscopy (AFM). We have generated quantitative maps of elastic modulus along myelinated and demyelinated axons, together with quantitative maps of axon topography. This study shows that AFM can combine functional and morphological analysis of neurological tissue at the level of single nerve fibers.