N-(11-Trimethylammonioundecanoyl)-O,O＇-didodecyl tripeptide bromides and N-(11-trimethylammonioundecanyl)-O-dodecyl tripeptide bromides formed a parallel P-sheet structure when they aggregated in water and in CCl4. The parallel beta-sheet was distinguished from the antiparallel counterpart by Fourier transform infrared spectroscopy because the former lacks a weak band at about 1690 cm(-1) that is characteristic for the latter. The FT-IR spectra of the aggregate in CCl4 remained unchanged if the solution was diluted to 0.01 mM, condensed to dryness, or heated to 60 degrees C, and hence, the beta-sheet was easily formed and thermodynamically stable. The parallel beta-sheet was also possible to transform into an antiparallel beta-sheet, for example, by mixing with another tripeptide-containing amphiphile whose tripeptide part had an opposite direction. Transmission electron microscope (TEM) and atomic force microscope (AFM) pictures revealed that the aggregate in CCl4 is a bundle of small filaments whose diameters are 70-80 Angstrom. Developed interpeptide hydrogen bonding should be formed along the long axis of the filament. The, morphological structures and stable peptide arrangements of the present assemblages are similar to those of the amyloid fiber whose accumulation causes fatal diseases.