In order to minimise the hair damage due to hair straightening process, post-treatment is recommended to protect the damaged hair from further depreciation and breakage. However, few reported quantitatively about the effectiveness of post-treatment after hair straightening process. Therefore, the aim of this paper will investigate the effectiveness of posttreatment methods for chemically straightened hairs. The effectiveness will be evaluated through different analytical methods such as scanning electron microscopy (SEM), diffuse reflectance spectrophotometry, tensile strength test and urea bisulphite solubility test for the properties related to morphological structure, hair colour change, tensile strength as well as chemical damage respectively. From the findings of the instrumental results, it was obvious that the application of post-treatments would improve the lustre of the damaged hair by giving higher value in lightness when compared with the raw hair control sample. Furthermore, the strength property of the post-treated hair increased when compared with the chemically straightened hair. This was due to the fact that the film-forming agents of conditioning products formed a protective layer and smooth surface on the fibre surface.