Two new nickel metavanadate hydrates, Ni(VO 3 ) 2 ·4H 2 O and α-Ni(VO 3 ) 2 ·2H 2 O, have been synthesized using a “chimie douce” process; their crystal structures have been solved from single-crystal X-ray diffraction data. The tetrahydrate Ni(VO 3 ) 2 ·4H 2 O crystallizes in the monoclinic space group C2/c with a unit cell of dimensions a=12.969(5) Å, b=9.817(3) Å, c=6.880(2) Å, β=112.14(3)°; Z=4; the structure was determined from 1055 independent reflections and refined until R=0.024 and R w =0.034. An orthorhombic cell has been found for the dihydrate α-Ni(VO 3 ) 2 ·2H 2 O: a=5.530(1) Å, b=10.621(10) Å, c=11.756(5) Å, Z=4, space group Pnma; the structure was determined from 1201 independent reflections until R=0.017 and R w =0.018. The structures of the two materials mainly differ in the vanadium environment in the (VO 3 ) n− n metavanadate chains. They are constituted of edge-linked VO 5 square pyramids in the tetrahydrate and from vertex-linked VO 4 tetrahedra in the dihydrate. As the hydrogen atoms were localized in these two compounds, all the hydrogen bonds existing in these structures were clearly evidenced.