It is important for the understanding of the complexity of a human hair structure to observe the ultrastructures and to measure their mechanical properties at the same point of the specimen. We examined the extremely smooth Surface of the hair cross-section by force modulation (FM) method and Young's modulus mapping method by analyzing force curves (FCs) in two-dimensional lattice being installed in an atomic force microscope (AFM). Consequently, the FM method was used to evaluate the changes in structural and mechanical properties in the internal structures of hair in air and in water performing any pre-treatment (chemical modification) on hair specimen. It was also possible to determine the semi-quantitative changes caused by the chemical damages of hair and the repairing effect of conditioning agents at nano-size level with Young's modulus mapping method. (C) Koninklijke Brill NV, Leiden, 2009