Recently it was established that bright green solution of potassium 2,6-diethoxycarbonyl-3,5-dimethyl-4-nitrosophenolate (С₁₄H₁₆KNO₆) (I) gave white sediment of 2,6-diethoxycarbonyl-3,5-dimethyl-4-nitrosophenol (presumably (С₁₄H₁₇NO₆)₂ (II) after an acid was added into solution. The crystal structures of both substances were established by X-ray powder diffraction technique. The unit cell parameters for (I): a = 9,3802(8) Å, b = 8,1442(6) Å, c = 20,5440(16) Å, β = 102,124(4)°, V = 1534,5(2) ų Z=4, space group P2₁/n and for (II): a = 10,7874(9) Å, b = 11,5314(11) Å, c = 12,1206(11) Å, α = 86,113(7)°, β = 77,920(8)°, γ = 86,381(7)°, V = 1469,1(2) ų, Z=2, space group P-1. Structure solution was carried out in direct space by the Monte Carlo method using hard and soft constrains on molecule geometry which making it possible to determine the structures with 22 and 42 nonhydrogen atoms using X-ray powder diffraction data. Structure refinement was carried out by Rietveld approach. The structure (I) represents molecular packing identical layers parallel to the plane (10-1). The distance between the layers is equal to 9,28 Å. In the layer at a distance of 9,38 Å of each other are zigzag chains of potassium cations, and organic anions is in the space between the chains. There is π-conjugation between phenol ring and nitrosogroups. in (С₁₄H₁₆NO₆)^- anion. Potassium cation is coordinated by irregular polyhedral, consisted of “free” oxygens of carboxyl groups, hydroxyl and nitroso groups and nitrogen of nitroso group. The space between the layers is filled by ethoxy groups which are not involved in the formation of additional H-bonds. The structure (II) represents the packing dimer nitrosophenol molecules (I). Dimerization occurs via bonding nitrogen atoms of nitroso groups according azidooxide type. There are no π- conjugations of benzene rings with nitroso groups as well as between themselves. An angle between the planes of benzene rings in the molecule is equal to 23^о and ones between each the benzene plane and the plane of (NO)₂ fragment are approximately 66^о and 84^о. The absence of the conjugation in molecule brings a flexibility which is appearing in molecular packing without possible centrosymmetry.