The reaction mechanism of PbMg1/3Nb2/3O3-PbZrO3-PbTiO3 (PMN-PZT) perovskite phase prepared by the columbite route has been studied in the temperature range from 600 to 800 degrees C. The effects of heating and cooling rate during the calcination of 3PbO + MgNb2O6 + PZT powder mixtures have also been investigated. Nearly pure perovskite phase, 0.9 PMN-O.1 PZT solid solution with no pyrochlore phase, as determined by X-ray diffraction, could be prepared at 800 degrees C for 2 h. From DTA/TGA, dilatometry and XRD data the reaction mechanism of PMN-PZT solid solution formation could be divided into three steps : (i) decomposition of columbite (MgNb2O6) by reacting with PbO at 350 to 600 degrees C (ii) the formation of a B-site-deficient pyrochlore phase Pb2Nb1.33Mg0.17O5.50 at close to 650 degrees C, and (iii) the formation of perovskite phase PMN-PZT solid solution from the reaction of Pb2Nb1.33Mg0.17O5.50 PYrochlore phase with MgO and PZT above 650 degrees C.