The co-operation behavior of iron and phosphorus in clectrodeposition of Zn-Fe-P alloy onto copper from light acid chloride solutions (LACS) was investigated by means of cyclic voltammetry and steady-state polarization techniques. It was found that, under the experimental conditions, the phosphorous and the iron promote the reduction of each other and their contents in Zn-Fe-P coating change synchronously, which has been interpreted theoretically in the view of quantum chemistry. The theoretical results showed that, because the orbital radius of 4S of iron atom is shorter than that of zinc atom, the overlapping integral of iron and phosphorus (SFe-P) is smaller than that of zinc and phosphorus (SZn-P) which resulted in the synchronous variation of the contents of the phosphorus and the iron in the electrodeposits, and which also showed that there exist the cooperative effect of phosphorus with iron series metal among their co-depositing coatings. (C) 2002 Elsevier Science B.V. All rights reserved.