This paper presents the synthesis and thermal behavior of double copper and potassium pyrophosphate, which can be used as a PK fertilizer containing copper as micronutrient. In order to find the conditions for the synthesis of this compound from copper sulphate and potassium pyrophosphate, various Cu2+:P2O74- molar ratios (0:1-2:1), various molar concentrations of the Solutions (0.075; 0.1; 0.15 and 0.2 mol L-1) and various temperatures (25, 50, 75 and 100 degrees C) have been used. The solid product synthesized in optimum conditions for the separation of micronutrient copper from the reaction mass (Cu2+ :P2O74-molar ratio 1:1, concentration 0.1 mol L-1) was subjected to a complex study: chemical analysis, thermal analysis, energy dispersive X-ray spectroscopy, scanning electron microscopy and X-ray diffractometry. During heating up to 1000 degrees C, K2Cu3(P2O7)(2)center dot 3H(2)O loses the crystallization water; several transformations of the phosphates also take place: the decomposition of pyrophosphates to ortho-phosphates; the transformation of ortho-phosphates; the polymerization of a fraction of ortho-phosphates to amorphous phosphates with longer chains; the reorganization of ortho-phosphates and poly-phosphates to pyrophosphates and their crystallization. The decomposition mechanism was confirmed when using the X-ray diffraction patterns of the compound, thermally treated at several temperatures. (C) 2009 Elsevier B.V. All rights reserved.