Borazine, a precursor for BN, was synthesized by a reaction of LiBH4 with (NH₄)₂SO₄. The composition and structure of the synthesized product was characterized and confirmed by GC-MS, FT-IR and 1H-NMR. Cured polyborazine was obtained by heating borazine at 80℃ for 72hrs and was converted to BN ceramic after pyrolysis. The pyrolysis behavior of polyborazine was investigated based on TG, FT-IR and XRD analysis. The results show that polyborazine still holds some B-H and N-H bonds, which will be continuously dehydrogenated when heated, and the ceramic yield is about 89.5％at 1400℃. Bonds of B-H are broken mainly before 800℃, while disappearance of N-H bonds occurs at much higher temperature. The inorganic extent is high and amorphous BN is obtained when polyborazine is pyrolyzed at 800℃, while h-BN is obtained when it is pyrolyzed at 1600℃.