Novel nanostructured liquid crystals (NLCs) based on poly(ethy1eneimine)s (PEIs) were synthesized by the use of linear PEIs, a liquid crystalline monomer cholesteryl 4-((2-bromopropanoyl)oxy)-2-fluorobenzoate, and some protonic acids such as trifluoroacetic acid, fluoboric acid, fluorophosphoric acid and so on. The chemical structure, liquid-crystalline behavior and electrorheological (ER) properties were characterized by means of various experimental techniques. The NLCs produce SmA and bicontinuous cubic (Cub_I) self-assembly structures. On cooling cycles, the SmA phase of the NLCs is formed from the isotropic state due to orientation of mesogens, while a bicontinuous cubic mesophase is formed due to interfacial curvature of polymer main-chains originating from the chiral structure, electrostatic attraction and ion aggregations of the ionic groups. Although Cub_I phases have been used in some interesting areas such as membrane applications, this work provides potential applications in the fields of ER fluids. The ER effect of the NLCs is illustrated according to the relationship between the nanostructure and the rheology.