Abstract: In order to determine the inhibitory activity of chito-oligosaccharides against common pathogens and the synergistic antibacterial effects of chito-oligosaccharides with five common antibiotics, in this experiment, the minimum inhibitory concentration（MIC） and minimum bactericidal concentration（MBC） of chito-oligosaccharides and streptomycin sulfate, tetracycline hydrochloride, tetracycline, doxycycline hydrochloride, neomycin sulfate against Escherichia coli CICC21482, Staphylococcus aureus ATCC6538P, Vibrio parahaemolyticus ATCC17802, and Vibrio Harveyi ATCCCBAA-1117 were determined. The synergistic antibacterial effect of chito-oligosaccharides and antibiotics was analyzed according to the fractional inhibitory concentration index（FIC index）. The results showed that chito-oligosaccharides had strong inhibitory activity against common pathogenic bacteria, and their MICs were between 22.5-45 mg/mL and MBCs between 45-90 mg/mL. The inhibitory effect of neomycin sulfate on Vibrio parahaemolyticus ATCC17802 was not observed, and no MIC and MBC were detected. Therefore, the combined drug sensitivity test of chito-oligosaccharides and neomycin sulfate on Vibrio parahaemolyticus ATCC17802 was not conducted. Chito-oligosaccharides showed no correlation with streptomycin sulfate and tetracycline on Vibrio parahaemolyticus ATCC17802, but showed partial synergistic and synergistic effects with streptomycin sulfate, tetracycline hydrochloride, tetracycline hydrochloride, doxycycline hydrochloride and neomycin sulfate, and had obvious synergistic antibacterial effect.The results suggested that chito-oligosaccharides had inhibitory and bactericidal effect on common pathogenic bacteria when used alone and in combination.