Abstract: This paper discussed the antibacterial effect of the worsted fabric treated with citric acid,chitosan and its derivatives,and the pictures of scanning electron microscopy(SEM) and Fourier transform infrared spectroscopy(FTIR) were employed to study the crosslinking mechanism and antibacterial mechanism of the treated fabric.The results show that the worsted fabric after treatment keeps good antimicrobial activity against staphylococcus aureus and esaherichia coli after 20 laundering cycles.