A water-quenching technique was adopted to evaluate the thermal shock behavior of hot-pressed ZrB2-SiC and ZrB2-SiC-graphite composites in an air atmosphere. The strength retention of the two kinds of composites was measured after varying temperature (Delta T-c) up to 1000 degrees C. Monolithic ZrB2-SiC showed rapidly drop in flexural strength above Delta T of 400 degrees C, however the critical thermal shock temperature difference (Delta T-c) is enhanced by adding graphite, and the ZrB2-SiC-graphite composite showed a higher retained strengths up to 1000 degrees C. The main reasons for a great improvement of thermal shock resistance (TSR) were also discussed and analyzed. (C) 2008 Elsevier B.V. All rights reserved.