A mathematical model has been developed to describe the electrodeposition of Fe-Ni alloys in the presence of an organic inhibitor. The model includes the mass transport of participating ionic species, homogeneous chemical reactions within the diffusion laver, the metal hydroxyl ion and inhibitor adsorption, and the associated electrochemical kinetics. The model can be used to predict the iron-nickel deposition rate (iron and nickel content in the alloy) as a function of the disk rotation speed, solution pH. and the bulk concentrations of the electroactive species and the organic additive. Model results indicated that in the presence of organic additive (saccharin) higher ferrous ion and nickel ion concentrations can be preserved at the interlace without concentration depletion within the diffusion layer. The model also predicted that iron content in the alloy increases by increasing the concentration of the additive and by increasing the electrolyte pH and disk rotation rate.