Hydrothermal synthesis of V2O5+TMA+LiOH in a 1:2:1 molar ratio after adjusting the pH with acetic acid to pH 3.3 resulted in the formation of a new vanadium oxide, TMAV8O20 . The new vanadium oxide has a monoclinic structure with space group C2/m and lattice parameters: a=23.655(2), b=3.5931(3), c=6.3175(5) Å and β=103.060(4)o . TMAV8O20has a layered structure with the vanadium atom in the octahedral sites and tetramethylammonium ions residing in between the vanadium layers.