ZrB2-60mol%SiC composite with a eutectic microstructure was oxidized at 1573 to 1873K with reduced total pressures (P-tot) and low oxygen partial pressures (PO2). The mass change was continuously measured by a thermobalance, and then fit with a multiple paralinear model. Oxidation scale of SiO2/ZrO2+SiO2/ZrO2/ZrB2 was formed at PO2>0.13kPa, whereas only porous ZrO2 remained at PO2<0.13kPa, P-tot<1.33kPa and higher than 1773K. With increasing PO2, the parabolic oxidation constant decreased, whereas the linear oxidation constant increased.