Magnetic field effects on the dynamic behavior of radical pairs generated in micellar solutions of benzophenone, naphthoquinone, and 2′,3′,4′,5′,6′-pentafluoroacetophenone were studied under high magnetic fields (⩽10 T). For the reaction of pentafluoroacetophenone, the lifetime of a radical pair and the yield of the escaped ketyl radical were found to increase steeply with increasing field strength from 0 to 2 T, but to decrease gradually from 2 to 10 T. For the other reactions, such a phenomenon was not observed. These new magnetic field effects were explained in terms of the relaxation mechanism and the molecular dynamics in micellar solutions.