The kinetics of NiAl3phase growth is studied on lateral diffusion couples in the temperature range from 375 to 450 °C. The lateral diffusion couple consists of an Al‐rich source on a Ni2Al3thin film. Analytical electron microscopy is used to determine the crystal structures and chemical compositions of the growing phases. The results show that: (1) Al is the dominant moving species in the growing NiAl3phase; (2) an equilibrium concentration of Al is established during the growth; and (3) the growth has a parabolic dependence on the annealing time. The study of NiAl3growth kinetics on lateral diffusion couples bridges the gap between bulk and thin‐film diffusion couples in terms of reaction temperatures. The activation energy of NiAl3growth is 1.2±0.2 eV.