We report for the first time a new single-walled carbon nanotube (SWNT)-induced lyotropic phase behavior of a F108 block copolymer/water system. As the concentration is increased by evaporation, the F108-SWNT/water system exhibits isotropic–hexagonal–FCC–BCC–lamellar transitions. This is in clear contrast with the F108/water system (isotropic–BCC–lamellar transitions), indicating that the hexagonal and the FCC phases are newly induced by the presence of one-dimensional SWNTs. The SWNTs maintain their individuality or very small bundle state in all the phases except the lamellar phase. In the hexagonal phase, the SWNTs are located in the hydrophobic core of F108 cylinders oriented parallel to the [001] direction. The epitaxial transitions between the phases allowed us to identify the possible orientation of SWNTs in each phase: [110] in the FCC and either ⟨100⟩ or ⟨111⟩ in the BCC. In the lamellar phase, the SWNTs exist most likely in the hydrophobic layers forming aggregations among them. This new SWNT-induced lyotropic phase behavior in a block copolymer system may provide a new scalable route to fabricate SWNT superstructures with well-defined architecture and new functionalities.