Magnetic minor hysteresis loops of compressively deformed Ni single crystals have been analyzed. We confirmed universal simple relations between magnetic parameters of minor loops, which are independent of dislocation density, crystal orientation, and the symmetry of crystal. The magnetic properties deduced from the relations are more sensitive to dislocations than those of the major hysteresis loop. Present results clearly show the great capability of minor loops for nondestructive evaluation of degradation in ferromagnetic materials.