Abstract: The Ni（Ⅱ） was reduced to Ni atom irreversibly by a onestep reaction in acetamideureaNaBr melt at 353?K. The α was determined 0.21 on Pt electrode and 0.18 on Cu electrode; the D0 was determined1. 15×10-8?cm2•s-1 on Pt electrode and 1.44×10-6?cm2•s-1 on Cu electrode. Although the Tb（Ⅲ）and the Mg（Ⅱ） can't be reduced to Tb and Mg alone, they can be inductively codeposited with Ni（Ⅱ） to obtain an amorphous TbMgNi alloy film by potentiostatic electrolysis. The content of Terbium in the alloy increase with the increasing of the molar ratio of Tb（Ⅲ）/Ni（Ⅱ） and the maximum was 87.88%. The content of magnesium in the alloy increase with the increasing of the cathodal potential and the maximum was 12.78%. Mg2Ni hydrogen storage alloy was obtained when the molar ratio of Tb（Ⅲ）/Ni（Ⅱ）and Mg（Ⅱ）/Ni（Ⅱ）were 3.4/1 and 8/1.

Key words: electroreduction, inductive codeposition, TbMgNi alloy film, amorphous alloy , acetamideureaNaBr melt