The oxidation of ZrB2 nanoparticles was observed at high temperature of 1500 degrees C under low oxygen partial pressure of 5 x 10(-2) Pa by an environmental transmission electron microscope. The results demonstrate that the oxidation starts on the surface of ZrB2 nanoparticles with decomposition of ZrB2 into ZrO2 and B2O3. The nucleation and growth of ZrO2 on the surface of ZrB2 proceed with B2O3 being evaporated.