A novel method for testing ultra-high-temperature ceramics (UHTC) at very high temperature (above to 2,200 °C) in air with an exposure time of several minutes is used. The well-known ZrB2 + SiC material shows a limited temperature of use in an oxidizing environment due to the low stability above 2,000 °C of any silica that is formed. A few new systems without silicon are proposed, starting with the Hf or Zr, C, B and rare earth elements. The choice of rare earths is motivated by the formation of oxides with melting points higher than 2,000 °C. The complex oxide scales formed during oxidation are accurately described, in terms of presence of porosity and gradients of composition. Similarities with the mechanism of oxidation described for ZrB2 + SiC materials are shown. A significantly higher thermal stability of rare-earth oxide containing ceramics compared to silica is highlighted. As a consequence, the protective capacity of the oxide scale is improved.