Self-assembly of small molecules through noncovalent interactions into nanoscale architectures has been extensively studied in supramolecular chemistry. However, it is still challenging to develop a biologically inspired self-assembly system that functions in water with complex structure and dynamics by analogy with those found in nature. Here, we report a new water-soluble cationic porphyrin that undergoes adenosine triphosphate (ATP)-templated self-assembly into right-handed double-helical supramolecular structures. Direct observation of the porphyrin-ATP assembly by transmission electron microscopy has been accomplished. The assemblies consist of superhelical fibers with length greater than 1 mu m and width similar to 46 nm. The chiral superhelical fibers show reversible disassembly to monomers upon hydrolysis of ATP catalyzed by alkaline phosphatase (ALP), and the nanofibers can be re-formed with subsequent addition of ATP. Moreover, transient self-assembly of a chiral double helix is formed when ALP is present to consume ATP.