A number of proteins form supramolecular protein aggregates called amyloid fibrils which self-assemble under appropriate conditions. We have used high-resolution atomic force microscopy to obtain detailed ultrastructural information on fibrils formed from the E46K mutant of the human α-synuclein protein, which is associated with Parkinson's disease. Two distinct fibril species were found; one with a height of 6.0 nm exhibiting no periodicity along its length, and the other with 7.4 nm height, revealing a periodicity of 46 nm, typical for the E46K mutant. We also determined the bending rigidity of these fibrils by analyzing the curvature of the fibrils from 2D AFM images. By integrating the details of the fibril morphological features and their mechanical characteristics, we propose a structural model for α-synuclein fibrils, consisting of 6 filaments in two different packing configurations, consistent with the measured data.