Full dense TiB₂ sintered bodies containing 2 mol%Y₂O₃-ZrO₂ up to 40 wt% were fabricated by glass encapsulation HIP method. Mechanical properties of these TiB₂-(2 mol%Y₂O₃-ZrO₂) sintered bodies were evaluated and compared to those of TiB₂-ZrO₂ sintered bodies, which were fabricated and evaluated in our previous work. Three-point-bending-strength of TiB₂-10-20 wt%(2 mol%Y₂O₃-ZrO₂) was 1160-1200 MPa, which is almost the same strength as that of TiB₂-10 wt%ZrO₂. Our previous work showed that the addition of 10 wt%ZrO₂ was effective in improving the bending strength of sintered TiB₂. In this work, it was found that the addition of 2 mol%Y₂O₃-ZrO₂ was more effective in improving the bending strength of sintered TiB₂ than the addition of plain ZrO₂, by the comparison of TiB₂-(2 mol%Y₂O₃-ZrO₂) and TiB₂-ZrO₂ strength. Vickers hardness of TiB₂-(2 mol%Y₂O₃-ZrO₂) was also higher than that of TiB₂-ZrO₂. On the other hand, higher fracture toughness was obtained in TiB₂-ZrO₂. These differences of mechanical properties between TiB₂-(2 mol%Y₂O₃-ZrO₂) and TiB₂-ZrO₂ were caused by the differences of monoclinic ZrO₂ content in the sintered bodies.