The effect of free carbon on the hotpressing behavior of boron carbide powders, flexural strength and toughness of hotpressed boroncarbide ceramic materials is studied. The composition, microstructure and fracture behavior of hotpressed ceramic materials were examined and analyzed using Xray diffraction and SEM. The experimental results show that density and properties of sintered materials are depended on additive carbon content in powders. For a certain hotpressing conditions, relative density, flexural strength and fracture toughness of the materials hotpressed from boron carbide powder with 7wt% carbon are 985%, 460 MPa and 765 MPam1/2,respectively. From the analyses of compositions and fracture surface, it is found that crack branching and blunting are the main reasons for flexural strength decrease and fracture toughness increase with the increase of the carbon content.