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We investigate the structure and properties of ceramic based on tetragonal zirconia (Y-TZP) containing low-modulus inclusions of hexagonal boron nitride (h-BN). (Y-TZP)(h-BN) ceramic samples with low h-BN content exhibit increased fracture toughness (K1C). The highest fracture toughness was observed for (Y-TZP)(0.5 wt % h-BN) ceramic: K1C = 12 ± 0.53 MPa m1/2. The increase in failure viscosity caused by incorporation of low-modulus inclusions (i.e., h-BN) is due to two dissipative mechanisms: the martensite transformation of the ZrO2 matrix and crack arrest at relatively weak interfaces between the matrix and low-modulus inclusions of h-BN. As the proportion of h-BN increases, the contribution of martensite transformation to the fracture toughness diminishes, a consequence of the grain size of tetragonal zirconia diminishing, which makes this phase stable.