Abstract In the work, the statistical distribution of Y2O3 particle size in the system Pt- Y2O3 is evaluated by STEM method. Mentioned materials were prepared by two-stage reduction of Pt, low-energy mechanical alloying, densed by HIP and more stage rolling. It was shown that there are particles of two size categories in Pt matrix. They are: large particles, clusters, and ZrO2 inclusions with the size of 1.1 - 12 ?m, which represent 0.7 % of nominal volume fraction. The second part is of the effective disperse Y2O3 particles with the size of 0.09 - 1.1 ?m, the volume fraction of which was 0.3 % of the nominal one. Thin foils were evaluated by the SEM method in the scope of statistical particle size distribution by use of Wadde¾s parameters. Selective electron diffraction was used to identify the phases Y2O3 [( 200), (511), (513)] and Pt [(200), (020), (220)].