epsilon-Poly-L-lysine (epsilon-PL), a natural biomacromolecule having a broad spectrum of antibacterial activity, was grafted on the wool fiber via the acyl transfer reaction catalyzed by microbial transglutaminase (mTGase) to develop a new strategy for antibacterial functionalization of proteinous materials. The effects of the concentrations of epsilon-PLs and mTGases on the graft yields were investigated. A coating of epsilon-PL that almost completely covered the scale profile on the wool surface was visualized by scanning electron microscopy (SEM) and further demonstrated in terms of Allworden's reaction characteristic of wool. Identifiable differences in lysine content and color depth among the stained wool samples reveal the changes in the surface composition and polarity caused by the incorporation of epsilon-PL onto the wool substrate, respectively. The ratio of bacteriostasis to Escherichia coli of the wool fabric grafting epsilon-PL reached 96.6%, indicating an excellent antibacterial effect. The application of epsilon-PL and corresponding mTGase-catalyzed grafting reaction would provide a worthwhile reference for antibacterial functionalization of proteinous materials in various forms.