Effects of a magnetic field (<= 0.5 T) on electroless copper metal deposition from the reaction of a copper sulfate aqueous solution and a zinc thin plate were examined in this study. In a zero field, a smooth copper thin film grew steadily on the plate. In a 0.38 T field, a smooth copper thin film deposited on a zinc plate within about 1 min. Then, it peeled off repeatedly from the plate. The yield of consumed copper ions increased about 2.1 times compared with that in a zero field. Mechanism of this magnetic field effect was discussed in terms of Lorentz force- and magnetic force-induced convection and local volta cell formation.