Chitosan, a biocompatible, biodegradable, nontoxic polymer, is prepared from chitin, which is the second most naturally occurring biopolymer after cellulose. Sorbyl chitosan and p-aminobenzoyl chitosan were synthesized working under high-intensity ultrasound and their antimicrobial properties were analyzed against Escherichia coil, Staphylococcus aureus and Aspergillus niger. The structures of the derivatives were characterized by FTIR spectroscopy and elemental analysis. The results indicated that the products had the effect of bacteriostasis and the antibacterial activity increased with increasing the concentration. Acylated chitosan had better inhibiting effect on S. aureus than others. It was also found that the antifungal activities of the derivatives were stronger than that of chitosan.