The reaction kinetics of the combustion synthesis of Mg2Ni from a powder mixture of magnesium and nickel has been investigated. The physical and chemical changes of the samples during the combustion synthesis were followed by scanning electron microscopy (SEM), electron probe X-ray microanalysis (EPMA), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) to derive a suitable rate equation. The observations revealed that the synthesis of Mg,Ni progresses homogeneously rather than topochemically, and not through an intermediate phase, with acceleration by liquid generation of the eutectoid phase. The result was that the most reasonable expression is a second-order irreversible equation, k(1-f)(2), with an activation energy of 165 kJ/mol.