Magnetic field effects (MFEs) on the triplet sensitization of p-aminophenyl disulfide were investigated in a sodium dodecylsulfate (SDS) micellar solution by means of a nanosecond laser flash photolysis technique at high magnetic fields up to 10 T. The yield of the escaped (P-aminophenyl)thiyl radical increased steeply with increasing magnetic field strength (B) from 0 to 1 T, but decreased gradually from 1 to 10 T. At 10 T, the yield of the escaped radical became similar to that at 0 T. The MFEs observed at both low (B less than or equal to 1 T) and high (1 T < B < 10 T) fields were simultaneously quenched by the addition of a paramagnetic Gd3+ ion, Thus, these reverted MFEs were interpreted by the relaxation mechanism through anisotropic hyperfine and Zeeman interactions.