A ternary Ni-Sn-B alloy film was successfully deposited on an iron plate through electroless plating. The Sn content and film thickness strongly depended on the concentration of Sn2+ ions in the plating bath. The prepared Ni-Sn-B alloy films were characterized by X-ray diffraction (XRD) and X-ray fluorescence analyses and X-ray photoelectron spectroscopy. The XRD results confirmed the crystal structure of the Ni-Sn-B alloy. When the Sn2+ concentration was between 0.03 and 0.07 mol L−1, an atomically ordered phase of Ni-Sn-B was formed. To estimate the chemical resistance, the prepared Ni-Sn-B alloy films were immersed in NaOH or H2O2 for 10 days, and only a small decrease in film thickness was observed after immersion. The results suggested that the atomically ordered phase of the Ni-Sn-B alloy contributed to chemical resistance.