Abstract: The exsolution of garnet out of Al₂O₃-rich clinopyroxene in the Mengzhong eclogite in Donghai, Jiangsu Province is studied.By an estimate of the pressure and temperature at which the mineral assemblages have developed during the various stages using geothermo-barometry, the P-T path is reconstructed for the formation and evolution of the eclogite.The result shows that it has undergone three stages of evolution:(1)The formaton of eclogite at mantle condition through the exsolution of garnet out of Al₂O₃-rich clinopyroxene due to the possible increasing of pressure and decreasing of temperature;(2)Tectonic emplacement of eclogite into the high amphibolite facies gneiss basement;(3)Retrograde metamorphism together with country rocks after the emplacement.