The mechanical properties of alumina have been successfully improved by adding isolated boron carbide particles of two different shapes. a KIc of 7.26±0.20 MPa·m1/2 for alumina-boron carbide whiskerlike composites and of 5.27±0.12 MPa·m1/2 alumina-boron carbide shardlike particle composites has been achieved. the fracture toughness of these composites is dependent on the volume fraction of the boron carbide particles as well as their size and shape. the flexural strength is also appreciably enhanced to a constant value with from 5 to 20 vol% boron carbide additions. the whiskerlike particles increase the flexural strength by 25% and the shardlike particles produce a 47% improvement.