Abstract: Chitosan (CS) was modified by amidation with 7-hydroxycoumarin to improve its water solubility and enhance the bacteriostatic property by reducing the hydrogen bonding between chitosan molecules. 7-Hydroxycoumarin was firstly acylated by oxalyl chloride as a linker, and then coumarin was grafted onto chitosan molecules through a non-homogeneous amidation reaction to produce 7-hydroxycoumarin acylation-modified chitosan (CS-C). The coumarin-modified chitosan products were characterized by infrared spectrometry (FT-IR), X-ray diffraction (XRD) instrument, and thermal gravimetry, etc., for the solubility, antibacterial activity, crystalline, and thermal stability. The results showed that the chitosan had been amidated by coumarin, and the modified groups were mainly in the NH₂ and chloride as well as ester bonds. The highest degree of substitution of NH₂ was found when the mass ratio of chitosan to coumarin was 1:3, and the solubility mass fraction of the CS-C-3 prepared in this case could reach 79% in a neutral environment. Its bacteriostatic property was better than that of CS, with a minimum inhibitory concentration (MIC) of 0.5 g/L for Escherichia coli and a MIC of 1 g/L for Staphylococcus aureus. A minimum bactericidal concentration (MBC) value of 4 g/L for E. coli and a MBC value of 2 g/L for S. aureus.