Oxidation of ZrB2-based ultrahigh-temperature ceramic composites containing 10, 20, and 30 vol% SiC was performed at 1900°C for 1 h in air. ZrB2–20 vol% SiC exhibited the highest oxidation resistance at this temperature and formed a dense coherent oxide scale after oxidation, whereas a strong degradation was observed for both ZrB2–10 vol% SiC and ZrB2–30 vol% SiC. In addition, cracks and spallation in the oxide scale were also detected for the latter materials. The oxidation behaviors of ZrB2–SiC composites were investigated. The effect of SiC content was analyzed and oxidation models were proposed to describe the observed microstructures.