The reaction of polycarbosilane with zirconium( IV) acetylacetonate proceeded at 573 K in nitrogen atmosphere by the condensation reaction of the Si-H bonds in polycarbosilane and the ligands of zirconium( IV) acetylacetonate accompanied by the evolution of acetylacetone, and then the molecular weight increased by the cross-linking reaction with a formation of Si-Zr bond. The obtained polyzirconocarbosilane showed higher ceramic yield than the polycarbosilane. Zirconium contained in the pyrolysed polyzirconocarbosilane was furthermore found to have the effect of inhibiting crystalline grain growth of beta-type SiC up to high temperature, so Si-Zr-C-O fibre, which was obtained by the use of polyzirconocarbosilane as precursor, showed high tensile strength up to high temperature.