Monolithic B4C ceramics and B4C-CNT composites were prepared by spark plasma sintering (SPS). The influence of particle size, heating rate, and CNT addition on sintering behavior, microstructure and mechanical properties were studied. Two different B4C powders were used to examine the effect of particle size. The effect of heating rate on monolithic B4C was investigated by applying three different heating rates (75, 150 and 225 degrees C/min). Moreover, in order to evaluate the effect of CNT addition, B4C-CNT (0.5-3 mass%) composites were also produced. Fully dense monolithic B4C ceramics were obtained by using heating rate of 75 degrees C/min. Vickers hardness value increased with increasing CNT content, and B4C-CNT composite with 3 mass% CNTs had the highest hardness value of 32.8 GPa. Addition of CNTs and increase in heating rate had a positive effect on the fracture toughness and the highest fracture toughness value, 5.9 MPa m(1/2), was achieved in composite with 3 mass% CNTs. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.