The Y3Al5O12 （YAG） nanocrystals were synthesized by ultrasound-assisted and ultrasound- microwave-assisted alkoxide hydrolysis precipitation methods. The structures and morphology of the YAG were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The synthesis kinetics of two kinds of YAG nanocrystals was investigated using differential thermal analysis and thermo gravimetric analysis （DTA-TG） at different heating rates in argon gas. The results show that two kinds of YAG precursors have one obvious endothermic peak at 315-600 K. The apparent activation energy of two kinds of YAG precursors was calculated using the Doyle-Ozawa and Kissinger methods, the coefficients of reaction order, frequency factor and kinetic equations were also determined. The average apparent activation energy for the YAG precursor prepared by ultrasound-microwave assisted was calculated to be 80.76 kJ.mol-1 higher than the YAG precursor prepared by ultrasound-assisted synthesis （56.56 kJ.mol-1）.
