Al2O3 ceramic matrix composites toughened with 3Y-TZP (yttria-containing tetragonal zirconia polycrystals) and oriented hexagonal shape alpha-SiC platelets were fabricated using slip casting and cold isostatic pressing. The effect of platelet aspect ratio and volume fraction on fracture toughness, and mode and microstructure of the final composite was examined. The fracture toughness of the reinforced-composites was evaluated using indentation in four-point bending test. Scanning electron microscopy and transmission electron microscopy were used to determine the microstructural details and dominant toughening mechanisms which occurred. Toughness measurement tests and detailed observations of microstructures and fracture surface profiles have led to the conclusion that multiple-toughening behaviour via transformation toughening, microcracking, crack deflection, load transfer and platelet debonding and pull-out, as well as thermal residual stresses have a significant contribution in improving the fracture toughness. A fracture toughness value as high as 11.2 MPa m(1/2) was achieved for the specimens sintered at 1600 degrees C for 3 h with a platelet addition of 30 vol%. (C) 1999 Elsevier Science Limited and Techna S.r.l. All rights reserved.