Seven samples of Al 2 O 3 -30 wt.% TiC composites were prepared by hot-pressing the Al 2 O 3 powder mixed with TiC particles of different particle sizes. Knoop and Vickers hardness measurements were conducted on these samples, respectively, in the indentation load range from 1.47 to 35.77 N. The load-independent hardness numbers were then determined by analyzing the relationship between the measured indentation size and the applied indentation load. It was found that the load-independent hardness number increases with the increasing TiC particle size, and this experimental phenomenon may be attributed to the effect of the residual internal stress resulting from the mismatch between the thermal expansion of Al 2 O 3 matrix and that of the TiC particles.