The effect of B4C particle size on the reaction behavior of TiC–TiB2 ceramic/Cu composites from a 40wt.% Cu–Ti–B4C system by self-propagation high-temperature synthesis (SHS) was investigated. It was found that increasing B4C particle size not only makes the ignition and self-sustainment of the SHS reaction difficult but also decreases the combustion temperature and combustion wave velocity. The reaction products are dependent on the B4C particle size. Favorable composites consisting of TiC, TiB2 and Cu phases could be obtained by the control of B4C particle size. The reaction path was explored through a delicate microstructure and phase analysis on the combustion-wave quenching method. From the reaction path, the effect of B4C particle size on the ignition behavior, combustion characteristics and products of the Cu–Ti–B4C system can be clearly clarified.