The spontaneous infiltration of BN-base powder mixture with molten aluminum was carried out to produce ceramic/metal composites. Ceramic phases were synthesized by the in situ reaction shown below. 2Al+2BN+Me→MeB2+2AlN where Me denotes a metal element (tantalum, niobium, zirconium or hafnium) . Each of these metal elements was mixed with BN powder. The spontaneous infiltration occurred in each system with a 3600 s holding at 1473 K, and neither pores nor cavities were observed in these specimens. After a 3600 s holding, TaB2 and NbB2 were completely formed together with AlN for [Ta, BN] and [Nb, BN] systems, respectively. These in situ formed particles were uniformly dispersed in aluminum matrix. In the case of [Zr, BN] and [Hf, BN] systems, however, residual MeB2 (Me: Zr or Hf) and BN were found. According to the differential thermal analysis, the heat of tantalum-aluminum and niobium-aluminum reactions, initiating at around 1200 K, can ignite a reaction including boron nitride. However, zirconium-aluminum and hafnium-aluminum reactions initiate at around 1000 K, and they do not ignite the reaction including BN. Hence, it took a longer processing time to complete the in situ reaction for specimens with [Zr, BN] and [Hf, BN] powder mixtures. The powder mixture of tantalum and boron nitride was infiltrated with molten aluminum at temperatures above 1173 K, and both tantalum boride and aluminum nitride were present as a result of the in situ reaction.