ZrB2 based ceramic matrix composites containing two kinds of SiC whiskers were produced at 1800 ℃ under a uniaxial load of 30 MPa by hot-pressing. The microstructure and mechanical properties of the two composites were investigated. The results show that the flexural strength and fracture toughness of composites are related with the aspect ratio of SiC whisker: the larger the aspect ratio is, the better of the properties of materials. The maximum flexural strength and the fracture toughness are 651 MPa and 5.97 MPa.m1/2, respectively. The mechanical properties, especially the fracture toughness, are much higher than that of monolithic ZrB2 and SiC particles reinforced ZrB2 composites due to the main toughening mechanisms of crack deflection, whisker bridging and pullout.