Zinc(II) complexes with the commercial auxin herbicides 2,4-dichlorophenoxyacetic acid (2,4D; C8H6O3Cl2) and 2-(2,4-dichlorophenoxy)-propionic acid (2,4DP; C9H8O3Cl2) were prepared and characterized. The formulae of the solid complexes Zn2(C8H5O3Cl2)3_5H2O (Zn-2,4D) and Zn(C9H7O3Cl2)2_1.5H2O (Zn-2,4DP) were established on the basis of the results of elemental analysis and Zn(II) determination.Water solubility of synthesized complexes at room temperature was examined. X-ray powder analysis was carried out. The discussion of IR spectra and conductivity data is presented. Thermal decomposition of these complexes in air was studied by TG, DTG, DTA and TG/MS methods with simultaneous analysis of the solid and gaseous products. The formation of complexes Zn-herbicide in the water solution by potentiometric pH titration was also investigated. The dissociation constants (pK) of 2,4D and 2,4DP were determined at 25°C and I = 0.1 (KNO3).