Crystalline surfactant molecular complexes serially obtained in both ionic surfactant systems of quaternary ammonium and pyridinium salts and of alkyl sulfate salts, provided abundant knowledge regarding not only the crystal structures by X-ray analysis but also solution behavior. In solution the surfactant molecular complexes behaved themselves as a novel surfactant species different from the mother`s, i.e., they presented their own cmc`s and inherent Krafft points. In addition, the observation of the yielding process of the crystalline surfactant molecular complexes from homogeneously solubilized solution systems offered significant keys to reconsider the fundamentals of “solubilization” as the followings that “solubilization” should merely be the dissolution systems of the surfactant complexes which were spontaneously generated in the processes. On the basis of the new ideas it has been clarified that we can always realize promptly any desired solubilized solution system, once we have, before hand, acquired the surfactant molecular complexes between the desired surfactant and the solubilizates which should afford us the desired systems. We applied this idea firstly to improve drug solubility enhancement and succeeded in modifying hardly water soluble drugs into instantaneously soluble ones.