Mathematical modeling of the combustion synthesis was studied theoretically and experimentally by taking Mg2Ni synthesis as an example. An unsteady two-dimensional mathematical model was constructed by reflecting drastic changes in thermo-physical properties from starting material of magnesium nickel mixture to a product of intermetallic compound and measured solid-phase reaction rate with/without melting. For validating the model experimentally, an end of the cylindrical sample of compressive powders was heated, and local temperatures of the sample were monitored. The comparison between calculated and measured temperatures showed plausible agreement when the model took partial melting effect of a eutectoid phase into the fundamental equations.