ZrB2 with different volume contents (30%, 35%, 40% and 45%) was in-situ synthesized in SiC matrix with silicon carbide (SiC), zirconium dioxide (ZrO2), boron carbide (B4C), water-soluble phenolic resin and carbon black as raw materials. SiC-ZrB2 composites were prepared via pressureless sintering. The effect of ZrB2 content on the microstructure and properties was investigated by X-ray diffraction, scanning electron microscopy, and electronic universal tests. The results show that the phase composition of the composites with different ZrB2 contents are SiC and ZrB2 with a little of B13C2. The grain size of ZrB2 increases, the particles interconnect, the density, mechanical properties and electrical conductivity of the composites increase when ZrB2 content increases. At ZrB2 content of 45%, the volume density, open porosity, relative density, flexural strength, vickers hardness and volume resistivity of the composites are 4.16 g/cm3, 0.27%, 95%, (332±17) MPa, (16±2) GPa and (2.35±0.7×10-6) Ω?m, respectively.