Simultaneous atomic-force microscopy (AFM) and friction-force microscopy (FFM) measurements were carried out to examine supramolecular structures in filamentous aggregates formed from synthetic C-tail peptide fragments of tan protein. The AFM/FFM images of the peptide filaments deposited on a mica substrate were very reproducible and stable during the scans. The AFM images of the sample barely showed helical structures in the filaments, but did not show the detailed substructures. The general appearance of the filamentous aggregates was similar to that obtained with transmission electron microscope. Also, the FFM images revealed a supramolecular structure unit and helical structures in the filaments more clearly than the AFM images. This implies that the supramolecular structure unit which forms the helical structures of the filaments could be characterized with the simultaneous AFM/FFM measurement.