Ionic self-assembled structures have been prepared successfully between di-(2-ethylhexyl) phosphoric acid (DEHPA) and hexamethonium hydroxide (HMO(OH)₂). The DEHPA/HMO(OH)₂ complexes show good surface activity at a wide mixing molar ratio of DEHPA to HMO(OH)₂ (ρ), within which the critical micellar concentration (cmc) is far below that of any single component. In bulk aqueous solutions, rich phase behavior was observed by varying c_DEHPA and c_HMO(OH)2. When the concentration of HMO(OH)₂ is in the range of 10–100 mmol L⁻¹, isotropic L₁ phases, birefringent L_α phases and a phase-separated region were successively observed with increasing c_DEHPA. At high c_HMO(OH)2 range (>78 mmol L⁻¹), a narrow L₁/L_α two-phase region with the L_α phase at the bottom was noticed between the single L₁ and single L_α phase regions. The rheological properties of the samples in the single L_α phase region at 2.6 ⩽ ρ ⩽ 2.8 are quite similar. Cryo-TEM and freeze-fracture TEM (FF-TEM) observations revealed the presence of multilamellar vesicles with flexible and even branched bilayers. At 2.2 ⩽ ρ ⩽ 2.6, however, the rheological properties are highly sensitive to ρ due to the sophisticated self-assembly behavior as proved by imaging studies and ²H NMR measurements. Closely-stacked flat structures which look like foams or cellular networks have been newly discovered. Interestingly, NaCl could arouse an L₁ to L_α phase transition due to the suppression of the effective area of the hydrophilic headgroups of the ionic complexes, leading to an increase of the critical packing parameter p. The viscoelasticity properties of the salt-containing L_α phases decreased with increasing salinity. We hope our research can provide new ideas for the construction of supramolecular materials by surfactant ionic self-assembly (SISA) strategy.