Al(5)BO(9)is a promising thermal sealing material for hypersonic vehicles due to its low density, theoretically predicted low shear modulus, and low thermal conductivity. However, experimental investigations on the mechanical and thermal properties of bulk Al(5)BO(9)have not been carried out. Herein, we report the mechanical and thermal properties of bulk Al(5)BO(9)prepared by spark plasma sintering of solid-state reaction synthesized Al(5)BO(9)powders. The bulk (B), shear (G), and Young's (E) moduli are 148 GPa, 85 GPa, and 214 GPa, respectively, which are close to the theoretical values. The Pugh's ratio G/B is 0.574, indicating its intrinsic damage tolerance, which is also revealed by Hertzian contact test. The Vickers hardness (H-v) is 10.8 GPa, being lower than mullite. The flexural strength, compressive strength, and fracture toughness are, respectively, 277 +/- 35 MPa, 814 +/- 75 MPa, and 2.4 +/- 0.3 MPa center dot m(1/2), which are close to those of mullite. Al(5)BO(9)has anisotropic coefficient of thermal expansion (CTE) in three crystallographic directions, ie alpha(a) = (4.40 +/- 0.21) x 10(-6)K(-1),alpha(b) = (7.11 +/- 0.18) x 10(-6)K(-1),alpha(c) = (6.70 +/- 0.29) x 10(-6)K(-1)from Debye temperature to 1473 K, which are underpinned by its structural feature, ie lower alpha(a)is resulted from the edge-shared AlO(6)octahedron chains along the [100] direction. The average CTE is (6.05 +/- 0.06) x 10(-6) K-1. The thermal conductivity declines with temperature as kappa = 1336.39/T + 1.97, consisting with predicted trend from Slack's model. The low thermal conductivity and low density guarantee Al(5)BO(9)a promising candidate as ceramic wafer in the seal structure for hypersonic vehicles.