Combustion synthesis of intermetallic−ceramic composite materials usually involves high combustion temperature as well as high temperature gradient. Gravity may play an important role in such systems when the liquid phase is present, and the intermetallic and ceramic phases have different densities. The combustion characteristics and microstructure may both be affected by gravity. Combustion synthesis of (1 − x)Ni3Al + xTiB2 composites, with the weight fraction x varying from 0.05 to 0.8, was carried out under normal gravity conditions. Both the combustion temperature and wave propagation velocity increased, and the propagation mode changed from unstable (x ≤ 0.2) to stable (x ≥ 0.4), as the TiB2 content increased. The combustion temperatures were higher than the melting point of Ni3Al for samples with x ≥ 0.4, resulting in a composite material consisting of ceramic TiB2 particles dispersed in a Ni3Al matrix. Owing to buoyancy of TiB2 particles in the denser molten Ni3Al phase, gravity was found to affect the microstructure of the composite, yielding a nonuniform distribution of phases. The phase separation distance calculated by using Stokes' law compared well with measurements.