The mono-urea derivative 3 derived from 4-(2-aminoethyl)-pyridine and dodecyl isocyanate gelled aromatic solvents, such as p-xylene, tetralin, and benzene, in the presence of Ag(I). The complex formation by the coordination of two equivalents of mono-urea 3 to Ag(I) and the intermolecular hydrogen bonding between urea groups plays important roles for the fibrous self-assembly followed by the gelation.