The present study investigates the oxidation behaviour in air of a structural ceramic composite with the following volumetric composition: 55% AlN–15% SiC–30% ZrB2. This kind of ternary composite is electroconductive (3×10−4 cm) and has significant strength (∼700MPa) and toughness (4MPam1/2) up to 1000 ◦C. Oxidation tests were carried out in a TG equipment from 700 to 1300 ◦C with exposition time of 30 h. Significant weight gain is observed at T > 1000 ◦C. In the range 700–900 ◦C, the process is dominated by the oxidation of ZrB2 into zirconia and boria and the kinetic is nearly parabolic. At temperatures in the range 1000–1100 ◦C, boria reacts with alumina forming aluminium borate and borosilicate glass and the kinetic largely deviates from parabolic behaviour. In the samples oxidized at temperatures in the range 1200–1300 ◦C, aluminium borate and mullite crystallize on the surface. The kinetics is para-linear in this temperature range but at 1300 ◦C, the rupture of the outer layer, results in accelerated damage of the sample. The composite is recommended for applications up to 1100 ◦C.