Supramolecular assemblies in ternary systems of alkyldimethylamine oxide (C(n)DAO, n = 12, 16)/cinnamic acid/D2O were investigated by small-angle neutron scattering, In the C(12)DAO/cinnamic acid/D2O system, prolate ellipsoidal micelles with axial ratios of 1.3 and 2.4 were formed at mixing molar ratios X ([cinnamic acid]/[C(n)DAO]) of 0 and 0.2, respectively. For the C(16)DAO/cinnamic acid/D2O system, lamellar layers with a bilayer thickness of 30 Angstrom existed in a solution at X = 0, while rodlike micelles with a cross-sectional diameter of 50 Angstrom were constructed at X = 0.2. Vesicles in solutions at X = 0.5-1 had multilamellar layers. The bilayer thickness was 23-30 and 35-36 Angstrom for C(12)DAO/cinnamic acid and C(16)DAO/cinnamic acid vesicles, respectively. The thinner bilayer thickness suggests that the tilt or random orientation of alkyl chains may occur in lamellar bilayers and membrane bilayers. The comb-shaped arrangement is also possible in membrane bilayers by C(n)DAO/cinnamic acid complex.