The two mechanisms of phosphorus incorporation with nickel in electroless plating nickel are studied using X-ray fluorescence spectrometer (XRF) and cyclic voltammetry (CV). The results of XRF and CV data on the effect of single and double complexing agents on deposition rate and deposit composition indicate that nickel chelates can catalyze phosphorus generation, i.e., the mechanism of interface complex heterocatalysis on phosphorus incorporation with nickel. Furthermore, the choice principle to complexing agents for low-phosphorus electroless nickel bath was proposed based on it. Additionally, the direct mechanism of phosphorus generation can explain how single sodium hypophosphite can be reduced on nickel substrate on the CV curve. Finally, the optimal condition for low-phosphorus electroless nickel plating baths was determined. The experimental results support the explanation of the proposed mechanism. (c) 2005 The Electrochemical Society.