To avoid introduction of milling media during ball-milling process and ensure uniform distribution of SiC and graphite in ZrB2 matrix, ultrafine ZrB2-SiC-C composite powders were in-situ synthesized using inorganic-organic hybrid precursors of Zr(OPr)(4), Si(OC2H5)(4), H3BO3, and excessive C6H14O6 as source of zirconium, silicon, boron, and carbon, respectively. To inhabit grain growth, the ZrB2-SiC-C composite powders were densified by spark plasma sintering ( SPS) at 1950 degrees C for 10 min with the heating rate of 100 degrees C/min. The precursor powders were investigated by thermogravimetric analysis-differential scanning calorimetry and Fourier transform infrared spectroscopy. The ceramic powders were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The lamellar substance was found and determined as graphite nanosheet by scanning electron microscopy, Raman spectrum, and X-ray diffraction. The SiC grains and graphite nanosheets distributed in ZrB2 matrix uniformly and the grain sizes of ZrB2 and SiC were about 5 mu m and 2 mu m, respectively. The carbon converted into graphite nanosheets under high temperature during the process of SPS. The presence of graphite nanosheets alters the load-displacement curves in the fracture process of ZrB2-SiC-G composite. A novel way was explored to prepare ZrB2-SiC-G composite by SPS of in-situ synthesized ZrB2-SiC-C composite powders.