Alkaline treatment (pH 12.0) and neutralization transform native catalase to component I(100% yield), and component II(yield, 59$) plus catalase renatured (yield 41%), respectively. The yields of components I and II are decreased with milder alkaline treatment. Renatured calatalse from alkaline solution (pH 9.9-12.0) shows approximately the same Sw,20 (sedimentation constant) value as the native one, but has been partially inactivated by 10-20%. Sw,20 value determination suggests that rod-shaped native catalase in neutral solution is split to approximately equal subunits (component I) of 1/3 size at pH 12.0, which is converted to the dimer (component II) of component I.