Lithium manganese (II) vanadate dihydrate, Li 2 Mn(VO 3 ) 4 .2H 2 O, has been prepared hydrothermally and characterized structurally from single-crystal diffraction data. It crystallizes in space group C2/m of the monoclinic system with Z=2 in a cell of dimensions a=19.286(5) 9, b=3.523(1) 9, c=8.164(2) 9 and β=105.38(3) o . The structure consists of [Mn(VO 3 ) 4 ] 2 - layers, built up from MnO 6 octahedra and VO 5 square pyramids, separated by Li + ions and water molecules. If the discharge rate is slow enough, Li 2 Mn(VO 3 ) 4 .2H 2 O can insert reversibly up to 2 Li per formula unit between OCVs of 2.6 V and 2.15 V, while a new, unidentified, phase is obtained after insertion of 4 Li. Upon oxidation, lithium deinsertion occurs at high voltage (above 4.4 V), leading to Li x Mn(VO 3 ) 4 .2H 2 O materials with x=<0.7. It is hidden by an important electrolyte oxidation. The Mn 3 + /Mn 2 + redox couple, associated to the lithium deinsertion/insertion process, was estimated at a high voltage value (between 3.5 and 4.5 V), due to the inductive effect of V V on the Mn-O bonds.