Fe-C-P alloy films were electrodeposited from an iron (II) chloride solution containing citric acid and phosphinic acid (hypophosphorous acid) at 323 K. Effect of phosphorus content on mechanical properties such as Vickers hardness, fracture toughness, and wear resistance was systematically examined and changes in mechanical properties were discussed based on the data measured by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. It was disclosed that the Fe-C-P alloy films had a martensitic phase with a body centered tetragonal structure. The Fe-C-P alloys showed excellent mechanical properties compared to Fe-C alloys as judged from the measurements of Vickers hardness, fracture toughness, and wear resistance. The oxygen content of the films decreased significantly with increasing concentration of phosphinic acid in the palting solution. Addition of phosphinic acid to the electrolyte is an effective way to reduce the oxygen content of the films. Excellent wear resistance of Fe-C-P alloy films is associated with higher hardness and improved fracture toughness as a result of codeposition of phosphorus which reduced the oxygen content of the films. (C) 2004 The Electrochemical Society.