In the system of a homologous series of sodium alkyl sulfates, including SLS (sodium lauryl sulfate) and other anionic surfactants with various phenols and other materials as additives, the surfactant molecular complex formation was obviously proved from results of X-ray diffraction experiment on their powdery specimens and from the elementary analysis such as UV spectroscopy. Especially, well-grown single crystals occurring in a SOS (sodium octyl sulfate)/2-naphthol system provided detailed structural knowledge of the anionic surfactant molecular complex to establish the unambiguous existence of those complex species. In comparison with previous results of the cationic surfactant molecular complexes, significant variation observed in the X-ray diffractograms of the anionic complex species deduced almost no change or only slight contraction of the unit cell of the anionic mother surfactant crystals along their longest lattice direction, while in all cationic complexes a clear expansion was involved associated with the additive intrusion into the surfactant crystal lattices. The remarkable features on the diffractograms of the anionic complex species also corresponded well to observations in which many sorts of anionic complex species were hydrated and the additive stability occluded in their mother surfactant crystal structure was very poor compared with the cationic complex species.