The magnetic properties of chemically deposited CoNiP films which had been deposited from an ammoniacal-tartrate-hypophosphite bath ([Co2+] + [Ni2+] = 0.1M) were changed by electrolysis, applied simultaneously with the autocatalytic plating. Coercivity decreased remarkably; saturation magnetization also decreased for the films plated from the bath with [Co2+]:[Ni2+] = 6:4, 5:5. The coercivity first increased and then drastically decreased for films plated from the bath with [Co2+]:[Ni2+] = 10:0, 9:1, and 8:2. The changes in coercivity were found to be due to the changes in crystallinity of the film, while the changes in saturation magnetization were found to be due to the changes in the film composition. The magnetic properties were changed by changing these parameters. Therefore, electrolysis performed simultaneously with autocatalytic plating is an effective method for controlling the magnetic properties of chemically deposited CoNiP films.