The N-aryl Chitooligosaccharides (COS) derivatives were firstly synthesized with Benzaldehyde, salicylal and 3,4-two hydroxy benzaldehyde, subsequently was quaternized to enhance its water solubility.The chemical structures of all COS derivatives were characterized by ATR-FTIR or ¹H NMR. The antibacterial studies of these COS derivatives were carried out by the inhibition zone diameters methods against E.coli, S.aurueus and P.aeruginosa bacteria. The antibacterial activity results showed N-3,4-two hydroxy benzaldehyde Schiff’s base COS > N-salicylal Schiff’s base COS > N- Benzaldehyde Schiff’s base COS> COS. In comparison to the COS derivatives chemical structure, it was found that the phenol hydroxyl group from N-aryl Schiff COS could improved the antibacterial activity, and the samller of its steric hindrance the more high of the antibacterial activity.