TiB2-B4C ceramic composites containing no additives were hot-pressed from a mixture of TiB2 and B4C powders containing 0 up to 100 mol%B4C (20 mol%). Hot-pressing was conducted at 1950°C for 3.6 ks under a pressure of 31.2 MPa in an Ar gas atmosphere. The mechanical and electrical properties were examined as a function of compositional change from TiB2 to B4C. TiB2-B4C composites containing 20-60 mol%B4C had a relative density of 97.4-98.9%, Vickers hardness of 23.8-27.2 GPa, flexural strength of 589-705 MPa, Young's modulus of 490-568 GPa, fracture toughness (KIC) of 6.46-8.05 MPa · m1/2. The mean surface roughness (Ra) was 25.6-30.5 nm and the electrical conductivity 0.30-3.96 MS · m-1. Thus, these composites possessed a high electrical conductivity and a smooth surface. Their mechanical properties were 1.5 times higher than those of pure TiB2 or B4C ceramics, and comparable to those of SiAION or hot-pressed Si3N4 ceramics. The present composites are suitable as ceramic mold materials, machinable by electrical discharge, corrosion-resistant electrode components, tool materials and high-temperature structural materials.