A guanidine-based oligomer grafted with a reactive cationic surfactant was designed and synthesized through Michael addition in an attempt to combine its antibacterial and emulsification properties. This was also an excellent and efficient strategy for preparing more kinds of guanidine derivatives. Fourier transform infrared spectroscopy, H-1-NMR, and C-13-NMR showed that the guanidine-based oligomer grafted with reactive cationic surfactant was synthesized successfully. The antimicrobial activity and antimicrobial mechanism were investigated with several approaches. The antimicrobial activity results indicated that the introduction of a cationic surfactant into the guanidine-based oligomer effectively raised the antimicrobial activity and showed a synergistic effect. The UV absorption at 260 nm was used to detect the dynamic antimicrobial process of the modified guanidine oligomer. Further, the results of scanning electron microscopy and atomic force microscopy implied that the antimicrobial mechanism of the modified guanidine oligomer changed the permeability of the cell membrane of the bacteria and caused the leakage of intracellular components of the Escherichia coli cells. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3489-3497, 2013