A combination of sol–gel Pechini method and flame synthesis was used to prepare yttrium aluminate glass microspheres with the garnet composition (YAG, 62.5 mol% aluminium oxide, 37.5 mol% yttrium oxide). Prepared glass microbeads were studied by optical microscopy, SEM, X-ray diffraction (XRD), differential scanning calorimetry (DSC) and high-temperature (HT) XRD analysis. Formation of YAG as the only crystalline phase was observed during HT XRD experiment in the temperature interval (750–1200 °C), with the onset of YAG phase crystallization in the temperature interval 860–870 °C and most prominent increase in the YAG phase content between 905 and 910 °C. The experimental data obtained by DSC analysis and the Johnson–Mehl–Avrami–Kolmogorov model were used for determination of crystallization behaviour of the studied system. The frequency factor A  = 5.2 × 10 48  ± 9.6 × 10 48  min −1 , apparent activation energy E app  = 1100 ± 10 kJ mol −1 and the Avrami coefficient m  = 4 were determined. The linear temperature dependence of nucleation rate, reaction-controlled crystal growth interface and a 3-D crystal growth were confirmed in the studied system.