Iron (Fe), nickel (Ni), and iron-nickel (FeNi) platings were carried out potentiostatically on rotating disk electrodes. The effects of boric acid on the iron and nickel reduction rates were evaluated. Experimental results support the surface competition of adsorption of ferrous and nickel ions on the electrode surface in FeNi alloy deposition. Boric acid prevents the electrode surface passivation on nickel reduction. Furthermore, boric acid acts as a surface agent and functions as a selective membrane which blocks the passage of the reduction of nickel but permits the reduction of iron in a retarded rate. The existence of boric acid alters the polarization behaviours in the FeNi system significantly.