In　our　previous　work,　a　nanostructured　oxide　dispersion　strengthened　(ODS)　Mo　alloy　with　a　high　density　of　non-stoichiometric　Y-Zr-O　nanoparticles　was　developed　as　fuel　cladding　material.　Considering　the　hostile　high-temperature　condition,　this　study　focuses　on　the　thermal　stability　of　non-stoichiometric　Y-Zr-O　nanoparticles　at　1400　°C　for　48　h.　Results　showed　that　non-stoichiometric　Y-Zr-O　nanoparticles　appeared　to　coarsen,　resulting　in　the　loss　of　coherency　with　the　Mo　matrix.　The　core/shell　structure　with　Y-rich　Y-Zr-O　oxide　cores　and　Zr-rich　shells　was　formed　by　Zr　diffusion　from　the　Mo　matrix　to　the　oxides/matrix　interface.　Together　with　Ostwald　ripening,　it　contributed　to　the　evolution　from　metastable　non-stoichiometric　Y-Zr-O　oxides　to　equilibrium　Y-Zr-O　oxides　with　a　partitioned　Y2O3　concentration　distribution.　Further,　the　Zr　addition　accelerated　the　coarsening　of　Y-Zr-O　oxides.　Zr-rich　Y-Zr-O　oxides　were　more　likely　to　coarsen　due　to　the　larger　equilibrium　solubility　of　the　Zr　element　and　diffusion　activation　energy　than　those　of　Y-rich　Y-Zr-O　oxides.　©　2022　Elsevier　B.V.