In the field of high-performance ceramic materials, boron carbide (B 4C) is regarded as an ideal choice for protective armor and military applications due to its exceptional hardness, wear resistance, and lowest density. Nevertheless, the difficulty in sintering B 4C, along with the trade-off between hardness and toughness, greatly limits its applications. To improve the performance of B 4C ceramics, this study utilizes Ketjen black (KB) with ultrahigh conductivity and specific surface area as an additive. The KB-derived conductive network enhances spark plasma sintering (SPS) efficiency while maintaining the ultrahigh hardness and lightweight nature of high-purity B 4C ceramics. Experimental results demonstrate that the resulting B 4C ceramics contain only a small amount of residual carbon, without forming any secondary phases. Notably, with the addition of 4 wt% KB, the ceramic density remains at a low level of 2.48 g/cm 3, while the mechanical properties show significant improvement. The Vickers hardness reaches 36.81 GPa, and the fracture toughness is 4.05 MPa·m 1/2. These combined properties represent one of the best performance levels currently achieved in high-purity B 4C ceramics. Additionally, the improved sintering performance enables the KB/B 4C ceramic to fully manifest its superior impact-resistance and anti-fragmentation capabilities. These findings provide valuable insights for the preparation and application of lightweight, high-performance B 4C ceramics.