Abstract: The quaternary ammonium salt derivatives of pectin were prepared with pectin as carrier and dimethyl octadecyl 3-(trimethoxysilyl) propyl ammonium chloride as active antibacterial monomer. The cross-linking reaction between pectin and organosilicon quaternary ammonium salt was conducted to immobilize antibacterial groups on the surface of pectin molecules, which broadened the application of pectin. The pectin derivative was characterized by Fourier transform infrared spectroscopy (FTIR), ¹H NMR, Zeta sizer nano series, and scanning electron microscope (SEM). The antimicrobial properties of the pectin derivative against selected microorganisms were tested by the quantitative suspension method. The results revealed that (1) N-Octadecyl dimethyl(3-trimethoxysilylpropyl) ammonium chloride can be fixed onto the surface of pectin through chemical bonds. (2) The zero potential of the pectin and the pectin derivative was pH 3.4 and pH 8.2, respectively, and the quaternary ammonium groups significantly increased the zero potential. (3) The pectin derivative significantly inhibited the growth of E.coil, S. aureus and C. albicans with the inhibition rate of 99.99% for 30 min. In conclusion, quaternary ammonium salt derivatives of pectin with good antibacterial activity can be prepared with this method, which provides a reference for expanding the application of pectin and improving its economic benefits.