Composites of SiCf/BN/SiC with micron Al₂O₃ filler were fabricated via precursor infiltration and pyrolysis method (PIP), and then their flexural strength, high-temperature dielectric and microwave absorbing properties were investigated. Results show that as the filler content increases from 5% to 20% the flexural strength of SiC_f/BN/SiC composites increases firstly and then degrades, and the maximum strength can reach 295 MPa. The real part and imaginary part of the complex permittivity of the composites increase with the rising temperature. Due to the introduction of Al₂O₃ filler the values and increasing range of the high-temperature complex permittivity can be significantly decreased with the rising temperature. The composites without filler show poor room- and high-temperature reflection loss (RL), however when the composite possesses 20% Al₂O₃ filler, the room-temperature RL values can be decreased to below -8 dB in the whole X band and its applicable thickness can expand to 3.0~3.5 mm. The RL values can reach -5~-8 dB at 700℃ for the composite with 20% Al₂O₃ filler of 3.0mm in thickness. The introduction of Al₂O₃ filler enhances the design margin for the practical application.