Ni-Fe alloys were deposited galvanostatically on the disk part of the platinum rotating ring-disk electrodes (RRDEs). Contents of nickel and iron were determined using the electrochemical stripping method. It was shown experimentally and explained theoretically that nickel deposition rate is inhibited as the ferrous ion concentration in the bath is increased. A mathematical model that includes the phenomenon of surface competition between FeOH+ and NiOH+ ions can quantify the inhibition of nickel deposition rate in the presence of ferrous ion species.