Helical mesoporous silica nanofibers with parallel nanochannels were synthesized in high yield via a novel seeding-growth method by using the achiral cationic surfactant cetyltrimethylammonium bromide (CTAB) as template without auxiliary additives. A general entropy-driven model taking into account the icelike structure water due to the hydrophobic effect was proposed to explain the formation of helical mesoporous silica nanofibers. It was indicated that helical silica mesostructures could result from a thick layer of highly ordered icelike water around thin silicate seed rods with a proper concentration, which was verified by the effect of various anions and organic additives on the formation of helical mesoporous silica.