The effect of three different sintering additive systems on densification of boron carbide powder was investigated. The sintering additives were Al2O3:Y2O3, AlN:Y2O3 and BN:Y2O3 compositions. Powder mixtures were prepared with 10 vol% of sintering aids following conventional powder technology processes. Samples were sintered by pressureless sintering at 2050 °C/30min in argon atmosphere. Sintered samples were compared to a sintered B4C without sintering additive. Samples were characterized by XRD to analyze the crystalline phases after sintering and SEM to observe the microstructure and the second phase distribution. YB4 and YB2C2 were identified in all samples, indicating a reaction between Y2O3, B4C and B2O3 present at the B4C particle surface. The best densification result was achieved with Al2O3:Y2O3 additive system, showing 92.0 % of theoretical density, low porosity and 15.2 % of linear shrinkage. But this sample showed the highest weight loss.