Dense sintered composites of TiB2 and ZrO2(2 mol% Y2O3) have been fabricated by hot isostatic pressing for 2 h at 1500 degrees C under 196 MPa. The ZrO2 particles in the composites consist of m- >> t-ZrO2. There is no reaction between TiB2 and ZrO2. Microstructures and mechanical properties are examined, in connection with increased ZrO2 content. The fracture toughness and bending strength of the composites with 30 mol% ZrO2 content are 11.2 MPa . m(1/2) and 680 MPa, respectively.