An electroless Ni‐Co‐P plating solution was developed for preparing soft magnetic thin films. In this plating process, the optimum bath composition and operating condition were obtained by investigating the effect of operating conditions on deposition rate, film composition, and magnetic properties. Soft magnetic films with low coercive force (lower than ) and high squareness (higher than 0.8) were prepared from these electroless Ni‐Co‐P plating processes. The alloy film deposited from the optimum bath condition consists of fine‐particulated crystallites.