The thermal stability of ZrB2-based composites containing SiC-chopped fibers was tested in a bottom-up furnace at 1200 degrees C, 1500 degrees C, and 1700 degrees C for 30 min. The oxidation behavior was studied by X-ray diffraction, scanning electron microscopy, and weight gain. The degradation induced by oxidation was also evaluated considering the strength decrease of oxidized bars. Baseline ZrB2-composites containing the same amount of SiC particles or SiC whiskers were tested in the same conditions for comparison.