The synthesis and X-ray diffraction study of the compound K 2[OsO2(C2O4)2] • 2H2O are performed. The compound crystallizes in the triclinic crystal system, space group P 1̄, a = 6.545(1) Å, b = 6.835(2) Å, c = 7.595(2) Å, α = 85.76(2)°, β = 65.33(2)°, γ = 71.14(2)°, and Z = 1. The osmium atom is located at the center of symmetry and has a distorted octahedral coordination formed by oxygen atoms: two oxygen atoms of the osmyl group occupy the apical positions [Os-O, 1.730(2) Å], and four oxygen atoms of the oxalate ions lie in the equatorial plane. The K+ cation is surrounded by ten oxygen atoms located at different K-O distances in the range from 2.787(2) to 3.158(2) Å. The assignment of the absorption bands in the IR spectrum of K2[OsO2(C 2O4)2] • 2H2O is performed. The electronic absorption spectra of the compound are recorded in different solvents, and the thermal behavior in air is studied. © 2007 Pleiades Publishing, Inc.