Well‐defined supramolecularhelicalnanofibers have been constructed by a rationally designed achiralmonomer in aqueous solution based on the 1:2 host–guest combination between cucurbit[8]uril and a 4,4′‐bipyridin‐1‐ium chloride (BPY+) salt derivative. The formed nanostructures could be adjusted by varying the concentration of monomer from helicalnanofibers to a pH‐responsive hydrogel.