The NbMo solid solution (denoted as (Nb,Mo)ss hereafter) matrix ceramic composites reinforced with 15vol.%, 30vol.%, 45vol.%, and 60vol.% ZrB2 particles were fabricated by hot-pressing sintering at 2400°C. The effect of the ZrB2 content on the isothermal oxidation resistance and the oxide scales microstructure evolution exposed at 800°C, 1000°C, and 1200°C was investigated. The experimental results showed that both temperature and ZrB2 content have an influence on the oxidation behavior. The oxidation resistance of ZrB2-(Nb,Mo)ss composites increased with increasing ZrB2 content and decreased with increasing oxidation temperature from the view point of parabolic rate constant. The oxide scales at 800°C-1000°C contained special film-like Nb2Zr6O17, acting as a barrier for oxygen diffusing inwards and resulting in low parabolic rate constant. However, no Nb2Zr6O17 layer was observed at 1200°C because the volatile MoO3 and the volume effect of ZrO2 destroyed the Nb2Zr6O17 protective layer which resulted in severe spallation and poor oxidation resistance. Possible oxidation mechanisms at different temperatures with varying ZrB2 content were discussed and related to the observed oxide morphologies.