Effects of a magnetic field on the kinetics of electroless nickel deposition were studied. y-Alumina powder was used as substrate and mechanical agitation ensured that deposition proceeded under chemical kinetic control. A reaction mechanism based on chemisorption was proposed for electroless nickel deposition and the effects of magnetic field were discussed. The results indicate that electroless nickel deposition is a free radical reaction and an induction period was found. Experimental results of the magnetic field effects on the reaction orders with respect to both the nickel ion and hypophosphite ion correlated well with the theoretical analyses. The effect was due to the spin rephasing between the singletphased and triplet-phased radical pairs of Ni+ . ~ and the hydrogen atom, respectively. The activation energy was decreased by the magnetic field because more singlet-phased radical pairs were obtained from the faster rephasing of triplet-phased radical pairs induced by the magnetic field. The empirical rate equations with and without the magnetic field were obtained. Change of frequency factors indicated that the spins of free radical pairs were different.