A novel additive based on alkylphenol ethoxylate sulphite was investigated in Zn-Mn electrodeposition on steel from a chloride bath. Electrochemical study via cyclic voltammetry showed that the tested additive increases the over-potential of the Zn deposition, resulting from strong adsorption of molecules additives on the cathode surface. Thus, Mn-rich alloy containing 16.3% of Mn is successfully co-deposited. The morphology and crystallographic structure of Zn-Mn co-deposits were analyzed using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD), respectively. SEM micrographs showed that Zn-16.3% Mn alloy obtained in the presence of the tested additive displays hexagonal pyramid morphology. XRD analysis exhibited that Zn-16.3% Mn alloy is monophasic with hexagonal close-packed ε-Zn-Mn phase.