We have synthesized an amphiphilic dumbbell-shaped molecule consisting of dodeca-p-phenylene and aliphatic polyether dendrons as flexible end groups. The molecular dumbbell in aqueous solution self-assembles into well-defined left-handed helical cylinders with a diameter (8 nm) of a molecular length scale and a pitch length of 5.6 nm, as confirmed by TEM. These elementary helical fibrils are further assembled to give left-handed superhelical fibers with lengths up to several micrometers. Such a well-defined helical arrangement of conjugated rod building blocks may provide a new strategy for the design of one-dimensional nanostructured materials with biomimetic, electronic, and photonic functions.