Abstract <p>Synthesis of precursor powders was performed by microreactor technique in a two-step microreactor with intensively swirled reagent flows. Ceramic samples (matrices) (1 – <i>х</i>)ZrSiO₄‒<i>х</i>ZrO₂ were obtained by sintering nano-sized precursor powders in the 1000–1300°C temperature range in air. X-ray phase analysis has shown that at a temperature of 1300°C, partial decomposition of zircon was observed with the formation of a silicon oxide. Their thermal behavior was studied by dilatometry, and the temperature coefficient of linear expansion was accessed. The chemical stability of the obtained ceramic matrices was evaluated by the method of prolonged leaching in distilled water, more precisely, by the release into the contact liquid of both matrix components (Zr, Si) and specially introduced radionuclides (¹³⁷Cs, ⁹⁰Sr, ¹⁵²Eu). The samples exhibited sufficiently high chemical stability, which allows us to consider them as a possible matrix material for immobilization of high-level waste.</p>