A study was made of the oxidation of pure zirconium boride and alloys of zirconium boride with molybdenum disilicide-(ZrB1.9)23MoSi1.1 and (ZrB1.7)13MoSi1.2-obtained by sintering a mixture of zirconium boride with 5 and 10% molybdenum disilicide. The rate of oxidation was determined from the time dependences of specimen weight and oxide film thickness. On the basis of the kinetic oxidation curves and microstructural analysis, conclusions are drawn regarding the nature of the resultant oxide films. Alloys of zirconium boride with molybdenum disilicide have high oxidation resistance at up to 1550°C as a result of the formation of a borosilicate film on the surface.