The present work is to clarify the fine structure of hair fiber components, especially Cell Membrane Complex (CMC) of cuticle. Hair fibers were treated with either hydrophilic N-acetylcysteine (NAC), thioglycolic acid (TGA) or hydrophobic tri-n-butyl-phosphine (TBP) for disulfide bond (SS) reduction. It was confirmed that the sulfhydryl residues (R-SH) were mainly produced in the CMC region by the initial reduction, being observed fluorescent from R-SH after labelled with N-(7-dimethylamino-4-coumarinyl)-maleimide (DACM). These reduced fibers were grafted with methyl methacrylate (MMA) by using lithium bromide and potassium persulfate system. The location of the grafted polymer in the fiber was determined as a low electron density region by a high resolution transmission electron microscopy. The grafted polymer was mainly observed in the CMC and the endocuticle of the TGA-reduced fiber, but not in that of the TBP-reduced fiber. Especially a homogeneous unstained layer was found in the middle region of the δ-layer of cuticle CMC of TGA-reduced hair. When hairs were prefixed with ruthenium tetroxide instead of osmium tetroxide, a structural change of the δ-layer to lamella-like structure were observed in the CMC of cuticle without graft copolymerization. These results suggest that the CMC consists of not only relatively hydrophilic regions containing SS linkages which the reduction brings about a large space for polymer uptake but hydrophobic lamella-like lipid layers.