Аннотация:Zemannite-like compound, BaNi2(SeO3)3·3H2O, was prepared hydrothermally. Its crystal structure was solved in hexagonal system, space group P63, with unit cell parameters a = 17.783(9) Å, c = 7.4722(19) Å, V = 2046.5(17) Å3, Z = 2. Infrared spectroscopy confirmed presence of SeO3 groups and water molecules in the wavenumber range 4000 − 500 cm-1. Peculiar magnetic subsystem of BaNi2(SeO3)3·3H2O is represented by isolated face-sharing dimers of NiO6 octahedra, which constitute a honeycomb pattern in the ab plane. Contrary to presumed dimerization of the magnetic subsystem, BaNi2(SeO3)3·3H2O appears to be robust three-dimensional antiferromagnet with negative Weiss temperature Θ = − 39 K and long-range magnetic order at Neel temperature TN = 26 K. These observations are fully supported by the density functional theory calculations.