A cyclic tetra-beta-peptide composed of three beta-alanine residues and a L-beta-homolysine residue having 10,12-pentacosadiynoic amide at the side chain was synthesized. The cyclic tetra-beta-peptide formed peptide nanotubes in CDCl3. The diacetylene units along the peptide nanotubes were polymerized by UV irradiation to obtain peptide nanotubes with polydiacetylene along the nanotube. TEM and AFM observations of the polymerized cyclic tetra-beta-peptides confirmed that the peptide nanotube structure was preserved after polymerization. (C) 2011 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 98: 155160, 2012.