Bulk Si 2 N 2 O/β-cristobalite composites have been fabricated by a hot-pressing method using Si 3 N 4 , SiO 2 and Li 2 CO 3 as starting materials. β-Cristobalite in the as-sintered composites is successfully stabilized to room temperature through incorporating N and Li into its structure. The introduction of β-cristobalite significantly improves the dielectric properties. Si 2 N 2 O/62vol.% β-cristobalite composite shows a low dielectric constant of 4.8 at 1MHz. In addition, the density, Young's and shear modulus, and strength of the composites decrease with the increase of β-cristobalite content. When the β-cristobalite content is up to 62vol.%, the flexural strength of the composite reaches 212MPa. The bulk Si 2 N 2 O/β-cristobalite composites show the combination of low density, excellent mechanical performance, low dielectric constant and loss tangent, indicating that they are promising high-temperature structural/functional materials.