For the first time, ZrC–ZrB 2–SiC ceramic nanocomposites were successfully prepared by a single-source-precursor route, with allylhydridopolycarbosilane (AHPCS), triethylamine borane (TEAB), and bis(cyclopentadienyl) zirconium dichloride (Cp 2ZrCl 2) as starting materials. The polymer-to-ceramic transformation and thermal behavior of obtained single-source precursor were characterized by means of Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). The results show that the precursor possesses a high ceramic yield about 85% at 1000 °C. The phase composition and microstructure of formed ZrC–ZrB 2–SiC ceramics were investigated by means of X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Meanwhile, the weight loss and chemical composition of the resultant ZrC–ZrB 2–SiC nanocomposites were investigated after annealing at high temperature up to 1800 °C. High temperature behavior with respect to decomposition as well as crystallization shows a promising high temperature stability of the formed ZrC–ZrB 2–SiC nanocomposites.