Abstract: The solubility of the components in the system {84,3%∑[Ca(ClO3)2+ Mg(ClO3)2]+15,7%∑[CaCl2+MgCl2]}-CH3COOH·NH2C2H4OH - H2O was studied by visually polythermal method. The system was studied using six internal sections, on the basis of which a polythermal solubility diagram of the system was constructed. The surface of the liquidus of the polythermal solubility diagram of the system is divided into the crystallization fields of ice, [Ca(ClO3)2·Mg(ClO3)2], [CaCl2·MgCl2], CH3COOH, CH3COOH·NH2C2H4OH and a new compound of the composition CaOHClO3·2NH2C2H4OH·2H2O. The above fields in the solubility diagram converge at four nodal non-invariant points. The compound was precipitated in the crystalline from the assumed area of its crystallization and identified by chemical, x-ray phase and thermogravimetric analysis methods. It was found that the largest volume in the solubility diagram belongs to the crystallization field CaOHClO3·2NH2C2H4OH∙2H2O due to its low solubility in comparison with other components of the system. Analysis of the radiograph of the initial components and the synthesized complex based on them shows that diffraction reflexes differ from each other, both in the value of interplanar distances and in the intensity of diffraction lines. Thermal analysis also confirms the identity of the new compound. The obtained data on the solubility of components in the studied system can serve as a scientific basis for obtaining a new complex active preparation based on calcium-magnesium chlorate defoliant and monoethanolammonium acetate.