[en] Highlights: • Precursors were synthesized by reactions of allyl amine, ZrCl₄, borane and the Grignard reagent (allyl-MgCl). • Ceramization processes of the ZrNCB precursors were analyzed and ZrC-ZrB₂ ceramics were obtained. • The obtained nanocomposite ceramics have good high-temperature stability up to 2000 °C with dense and nano scaled structure. • The ZrC-ZrB₂ ceramics also have excellent stability at 1700 °C under air due to the oxidation layer formed on the surface. In order to prepare ZrC-ZrB₂ nanocomposite ceramics with high temperature stability from single-source precursors, the reactions of ZrCl₄, allyl amine, allyl-MgCl and borane were employed to synthesize suitable precursors. The meliorated ZrNCB precursor had favorable solubility and higher ceramic yield (68.8 wt%), which was then transformed to ZrC-ZrB₂ ceramics at different temperatures. The main phase of the ceramics was amorphous at 1000 °C. As the temperature increased, the amorphous phases started to crystallize, resulting in the appearance of ZrC and ZrB₂ peaks. The content of ZrC and ZrB₂ phases was relatively high in the nanocomposite ceramics at 1600 °C (over 80 wt%). The ZrC-ZrB₂ nanocomposite ceramics showed good high temperature stability up to 2000 °C. Oxidation test indicated that an oxide layer was formed on the ceramic surface at 1700 °C under air to prevent further oxidation of the ceramics. With excellent high temperature and oxidation resistances, the ZrC-ZrB₂ nanocomposite ceramics have potential application for advanced rocket engines and nuclear industry.