A chiral octadecavanadate has been isolated and optically resolved into enantiomers by spontaneous resolution. From the partial oxidation reaction of a reduced decavanadate [V10O26](4)(-) with nitric acid, a chiral octadecavanadate encapsulating a nitrate template was formed. A nitrate anion was incorporated at the center of the spherical polyoxovanadate cage. The structure may be regarded as a double helical V8 ribbon between two square pyramidal (VO5)-O-VI units, consisting of half-pitch helix with ca. 11.0 angstrom diameter and a half pitch length of 8 angstrom.