The use of protein-crosslinking enzyme, transglutaminase, as a biocatalyst in the processing of hair offers a variety of exciting and realistic possibilities which include improving the rigidity of hair fibers. Among the transglutaminases from many different living organisms, the microbial enzyme prepared from Streptomyces mobaraensis, significantly increased the tensile strength of hair by 15.64% compared to a control when it was applied to damaged hair. This indicates that transglutaminase can restore the negative effects of washing hair with shampoo. Also transglutaminase improved the characteristics of hair surface, which could be useful for increase of luster and reduction of friction force of hair surfaces.