The formation of a Cr-free conversion layer on hot-dip galvanized (HDG) steel involves various interfacial processes which radically influence the composition of the coating and thus its performance. Here, we investigate the role of the main constituents contained in the treatment bath, the polymeric compounds and manganese phosphate species, by using derivative versions from the standard solution. A detailed X-ray photoelectron spectroscopy (XPS) analysis allowed distinction between oxygen originating from polymeric compounds and oxygen of inorganic nature in oxides/hydroxides or phosphate species. Our results revealed that manganese phosphate present in the treatment bath promotes the polymer adsorption on HDG substrate. Angle-resolved XPS and depth profile showed the presence of TiO2 layer on the outer part of the conversion layer, when polymeric compounds are not detected.