Four kinds of composites, ZrB2-SiC, ZrB2-SiC-ZrC, ZrB2-SiC-ZrN and ZrB2-SiC-AlN, were synthesized in situ via reactive hot pressing (RHP) and reactive spark plasma sintering (R-SPS), using Zr, Si, B4C, BN and Al as raw materials. The synthesis process plays a critical role in the microstructural features of the composites obtained. The R-SPS process can lead to a more homogeneous and finer microstructure due to its high heating rates and short holding time, while the RHP process is likely to result in coarse microstructures due to a long enough holding time for grains growth. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.