A polyborosilazane, which is a precursor of ceramic fibre, was synthesized from perhydropolysilazane and trimethyl borate. The polyborosilazane was dry-spun and then pyrolysed to produce amorphous Si-B-O-N fibre. The Si-B-O-N fibre retained its high tensile strength to higher temperatures (about 1600-degrees-C). The fibre has a density of 2.4 g cm-3, tensile strength of 2.5 GPa and an elastic modulus of 180 GPa.