The microstructural evolution of composites of SiC/Cu-Si alloys obtained through process of reactive infiltration to 1400 degrees C was studied. Three zones were detected in the obtained composites: the reaction zone, the transition zone and the infiltrated zone. In the reaction zone and transition zone the resulting microstructure was composed of a metallic phase, graphite laminae and SiC particles. It was found that SiC decomposes into these areas because of the alloy Cu-Si, so the available Si forms a liquid solution that a room temperature consisted of a a solid solution and a gamma phase (Cu(5)Si). The carbon resulting from the decomposition of SiC precipitated as graphite laminae. In addition, the SiC decomposition was decreasing as the initial amount of Si in the alloy increased.