Influences of pH, temperature, and composition of bath on the deposition rate and the magnetic properties were studied for two kinds of electroless Co-P plating bath. The results obtained are as follows. Ammonia alkaline citrate bath was more stable than ammonia alkaline tartrate bath, and the film deposited from citrate bath gave a higher squareness. The magnetic properties of the film obtained from citrate bath greatly depended upon pH. Under the optimum conditions, the film deposited from citrate bath had coercive force of 330 Oe and squareness of 0.67. However the films deposited from tartrate bath had coercive force of 300 Oe and squareness of 0.58.