We describe simple procedures for fabricating single polymeric helical nanofibers and converting these helical nanofibers into linearly oriented nanofibers using a modified electric field in an electrospinning system. Helical structures were made from a solution of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) in water and ethanol by bending instability of electrospinning. By newly introducing parallel subelectrodes that change an ordinary electric field into a splitting electric field, it was elucidated that the tensional electrostatic forces caused by a modified electric field have an important effect on the transformation of helical structures.