Abstract: A modified phosphate coating on C/C composites used for aircraft brakes was made from zinc chloride, phosphoric acid, zinc phosphate and aluminum phosphate. In order to study the properties of the modified coating, an unmodified phosphate coating and a ceramic coating, which principally consists of silicon and boron, were also investigated. Results showed that all three coatings had excellent oxidation resistance at 500℃ for 100h and the maximum mass loss is 1.25%. The mass loss of the C/C composite with a modified phosphate coating was 1.76% when the composite was subjected to oxidation at 700℃ for 30h in air, and the value was 1.98% when the composite was subjected to thermal shock in air for 30 cycles (from 900℃ for 3min to at room temperature for 2min) followed by shock in air for 10 cycles (from 1100℃ for 3min to room temperature for 2min). The performance of the modified phosphate coating is the best among the three coatings. It has excellent oxidation resistance and thermal shock resistance.