Abstract: Porous BN/Si₃N₄ ceramics with high strength and low dielectric constant were prepared by tert-butyl alcohol (TBA)-based gel-casting method and pressureless sintering process at 1750 ℃ for 1.5 h in flowing nitrogen. At a fixed solid loading (15%, volume fraction) of the initial slurry, the influence of boron nitride content on the porosity, phase and microstructure was discussed. The relationships among flexural strength, dielectric constant and microstructure were also discussed. The results show that porous BN/Si₃N₄ composite ceramics with high porosity ranging from 55.1% to 66.2% are prepared by adjusting the content of BN. Dielectric constant of porous BN/Si₃N₄ composite ceramics is between 3.39 and 2.25, which shows a decreased trend with the content of BN increasing. Flexural strength decreases with BN content increasing, flexural strength reaches the maximum value (74.8±4.25) MPa, when the mass fraction of BN is 2.5%.