A reaction model has been developed to account for the mechanism of Zn‐Ni alloys deposition from acidic sulfate electrolytes. The heterogeneous reactions imply the presence of four adsorbates: (i) which catalyzes nickel deposition, (ii) the intermediate Had involved in hydrogen evolution which occurs at low polarizations on nickel‐rich deposits, (iii) the intermediate adion acting as a catalyst for the deposition of the zinc‐rich δ‐phase which prevails at high polarizations, and (iv) the anionic species which inhibits the formation of the δ‐phase. In the transition region of intermediate polarizations, an increase in the interfacial pH facilitates the chemical incorporation of S in deposits, which is catalyzed by the anionic adsorbate. The model validity has been confirmed by comparison with experimental polarization curves, electrode impedance measurements, and analyses of the deposit structures and compositions.