A　novel　amphipathic　chitosan　derivative,　N-benzoyl-O-acetyl-chitosan　(BACS),　was　prepared　by　using　the　selective　partial　acylation　of　chitosan　(CS),　benzoyl　chloride,　and　acetic　acid　under　high-intensity　ultrasound.　The　chemical　structure　and　physical　properties　of　BACS　were　characterized　by　FTIR,　H-1　NMR,　TGA,　and　XRD　techniques.　The　degrees　of　substitution　of　benzoyl　and　acetyl　for　the　chitosan　derivatives　were　0.26　and　1.15,　respectively,　which　were　calculated　from　the　peak　areas　in　NMR　spectra　by　using　the　combined　integral　methods.　The　foaming　properties　of　CS　and　BACS　were　determined　and　the　results　suggested　BACS　had　better　foam　capacity　and　stability　than　those　of　chitosan.　In　addition,　the　antimicrobial　activities　of　CS　and　BACS　were　also　investigated　against　two　species　of　bacteria　(Escherichia　call　and　Staphylococcus　aureus)　and　a　fungus　(Aspergillus　niger),　the　results　indicated　that　the　antibacterial　and　antifungal　activities　of　BACS　were　much　stronger　than　those　of　the　parent　chitosan.　These　findings　suggested　that　BACS　was　preferable　for　use　as　a　food　additive　with　a　dual　role　of　both　foaming　agent　and　food　preservative.　(C)　2015　Elsevier　B.V.　All　rights　reserved.