Flexural strength, elastic modulus, and hardness were used to characterize the mechanical properties of ZrB2-SiC composites that contained varying SiC particle sizes. Dense ZrB2-SiC composites consisting of 70 vol% ZrB2 and 30 vol% alpha-SiC were produced via hot pressing. This series of composites had maximum SiC particle sizes that ranged from 4.4 to 18 mu m. The mechanical properties scaled with the maximum SiC particle size, not with ZrB2 grain size. Flexural strength decreased as the maximum size of SiC particles increased from 1150 MPa at 4.4 mu m to 245 MPa at 18 mu m with an abrupt decrease in strength at similar to 11.5 mu m. Elastic modulus remained constant at similar to 530 GPa for compositions containing SiC particles smaller than 11.5 mu m, but exhibited a decrease with larger SiC particle sizes. Vickers and Knoop hardness were 21.4 and 17.2 GPa, respectively, for ceramics with SiC particle sizes <11.5 mu m, but hardness decreased for larger SiC particle sizes. The decreases in strength, elastic modulus, and hardness with SiC particles larger than 11.5 mu m were coincident with stress-induced microcracking in the composites.