Previous studies showed that iron‐molybdenum alloys could be deposited from pyrophosphate solutions. This investigation shows that a similar bath can be used to deposit cobalt‐molybdenum alloys. The addition of hydrazine sulfate to the plating bath prevents anodic oxidation of Co (II) to Co (III). It also causes an increase in the cathode current efficiency and in the molybdenum content of the deposits. Efficiency is further increased by wiping the cathode during plating. The average content of the deposits was about 56% molybdenum, 37% cobalt, and 7% nonmetallic material. The cathode current efficiency was about 46%. The deposits were bright and adherent but tarnished readily unless a protective coating was applied.