Submicron powder Y3Al5O12 (YAG) aluminium yttrium garnet was synthesized from an Al-Y-ceramic-forming precursor, according to the method developed in the State Research Institute for Chemistry and Technology of Organoelement Compounds (SRICTO). The advantage of the method is the possibility of obtaining close to the stoichiometric phase and obtaining high purity nanopowder. In this work, we studied the effect of the pyrolysis temperature of the polymer (700°, 800° and 900°C) and grinding time on the rheological properties of the powder. It was shown that after pyrolysis at 700° and 800°C, the powder has an amorphous structure, the ultimate strain, in this case, being 6.1 and 8.1% of the initial size. The compressibility modulus decreases with increasing temperature from 34.5 to 19.4 MPa. Due to the formation of YAG crystals after pyrolysis at 900°C, the compressibility of the powder increases and the compacts become denser.