Boron-rich boron nitride (BN) films have been prepared on Si and SiO2/Si substrates by the vacuum pyrolysis of spin-coated polyborazine films. physical properties of the prepared films such as film strength, thermal conductivity, and dielectrics were determined. The BN films vacuum-pyrolyzed at 900 degreesC showed residual N-H bonds with a 0.75 N/B ratio, interdiffusion phenomena, and preferred orientation at the interfacial zone. Hardness and the elastic modulus of the film increased to 1.6 GPa and 50 GPa by nanoindentation loading. It had a thermal conductivity of 134 W/(m.K) at 296.5 K, and a dielectric constant in the range of 5-7, with tan partial derivative between 0.01 and 0.47, depending on the film thickness.