Two samples of Ultra-High-Temperature Ceramic Matrix Composites, with carbon fibers in a ZrB2-SiC matrix, were exposed to supersonic dissociated air flow, simulating the atmospheric re-entry environment, in an arc-heated facility at specific total enthalpies up to 20 MJ/kg. Surface temperatures, exceeding 2400 K, were monitored by non-intrusive infrared equipment, which allowed detecting thermo-chemical surface instability phenomena. A zirconium oxide layer formed on the surface, below which the original material is perfectly preserved. Numerical simulations allowed describing the flow field around the samples and characterizing the materials behavior, in terms of thermal conductivity, catalycity and oxidation effects at high enthalpies.