[en] The method of sampling sodium vanadates with variable concentration has been used for studying interaction of deca-, meta-, pyro-, and orthovanadates of sodium with cobalt nitrate in aqueous solutions. The methods of potentiometry, solubility, X-ray diffraction, spectroscopy in visible and infrared regions, and thermography have been used for identification of the interaction products. It has been established that the composition of the interaction products depends on the nature of vanadate-ions and the ratio between the initial components. Interaction of cobalt nitrate with sodium decavanadate yields Na₄CoV₁₀O₂₈x23H₂O and Co₂V₄O₁₂x8H₂O; with metavanadate Co₂V₄O₁₂x8H₂O and Co₄(OH)₄V₄O₁₂x7H₂O; with pyrovanadate Co₂V₄O₁₂x8H₂O, [Co₃(OH)₄]₂V₄O₁₂x2H₂O, and Nasub(6x-8)[Co(OH)sub(x)]sub(6)Vsub(4)Osub(12)xaq, where x changes from 1.33 to 1.60; and with orthovanadate [Co₃(OH)₄]₂V₄O₁₂x2H₂O and Na[Co(OH)sub(1.5)]sub(6)Vsub(2)Osub(7)