Mechanical properties and thermal shock behaviour of slip-cast alumina-mullite refractories have been investigated. There was a marked improvement in strength, Young's modulus and fracture toughness values with the addition of finest (approximately 5 mu-m) mullite particles. The shorter length needle-like mullite particles led to some pull-out and crack deflection. More fracture surface energy was therefore required to connect the cracks for propagation, resulting in a high value of fracture toughness. The resistance to fracture initiation and propagation caused by the thermal stresses was increased, as supported by the R and R-st parameters. Therefore, the retained strength was improved by increasing the quench temperature, showing a high resistance to thermal shock. (C) 2002 Elsevier Science Ltd and Techna S.r.l. All rights reserved.