As part of our current studies of oligomeric amphiphiles, two trimeric surfactants containing three dodecyl chains and three quaternary ammonium headgroups connected by 1,3-propanediyl groups, the methyldodecylbis[3-(dimethyldodecylammonio)propyl]ammonium tribromide and trichloride, referred to as 12-3-12-3-12,3Br(-) and 12-3-12-3-12,3Cl(-) have been synthesized and purified, and their micellization behavior has been investigated in aqueous solution. On a weight/volume basis, the cmc’s of the trimeric surfactants are well below those of the corresponding monomeric and dimeric surfactants (dodecyltrimethylammonium bromide, or DTAB, and 1,3-bis(dodecyldimethylammonio)propane dibromide or 12-3-12,2Br(-)), whereas the micelle ionization degrees of the monomeric, dimeric, and trimeric surfactants are rather close. At a given concentration (weight/volume basis), the solution of 12-3-12-3-12,3Br(-) is much more viscous than that of the corresponding monomeric and dimeric surfactants, indicating a much stronger tendency to micelle growth. Measurements of micelle aggregation numbers at low surfactant concentrations supported this conclusion.