Stable carbide particles of TiC, ZrC and TaC were in situ synthesized in liquid aluminium by the reaction between Al-Ti, Al-Zr or Al-Ta systems liquid alloy and SiC or Al4C3 particles. It was possible to generate TiC particles of nearly 1 mu m diameter, even utilizing SiC of 14 mu m. However, the dispersion behaviour of TiC particles in the matrix depended on the size of the raw carbide. Finer SiC made the dispersion of TiC particles more uniform, resulting in a greater improvement of the mechanical properties. Furthermore, although Al-Ti-Si system intermetallic compound was detected in a TiCp/Al-Si composite fabricated by the melt-stirring method, those compounds consideraby decreased in the composite fabricated by the in situ method. The mechanical properties of in situ formed TiCp/Al-5 wt % Mg and TiCp/Al-5 wt % Cu composites were better than those fabricated by the melt-stirring method a nd by T6 heat treatment, the properties of in situ formed TiCp/Al-5 wt % Cu composite were further improved. The experimental results were analysed by the reaction model based on the assumption that the overall reaction rate was controlled by both the reaction and the diffusion.