The conditions for the preparation of Fe-Mo, Co-Mo, and Ni-Mo amorphous alloys by an electroplating technique were investigated. Mo is deposited as alloys when the iron family transition metal is in the plating solution, and when the concentration of Mo in the deposited film exceeds a certain limit the deposited alloy film becomes amorphous. The range of Mo concentrations required to produce an amorphous structure is 10∼55 at% Mo for Fe, 15∼55 at% Mo for Co, and 30∼75 at% Mo for Ni, but these ranges may be wider under certain circumstances. The most important condition for preparing amorphous alloys by electroplating is apart from plating temperature, not in the plating conditions, but in the composition of the deposited alloy, which is approximately the range in which intermetallic compounds are formed.