Abstract: The inhibitory effect and induced resistance of chitooligosaccharides from housefly larvae to black shank, Phytophthora parasitica var. nicotiana, were tested indoors.The results showed that chitooligosaccharides could inhibit the fungus, the inhibitory effect improved with the increase of chitooligosaccharides concentration within a certain range. The inhibitory efficiency of chitooligosaccharides at 1.0mg/mL was up to 97.0% in 10 days after application.In vitro test demonstrated that chitooligosaccharides could also induce the resistance of tobacco inoculated with the fungus the induced efficiency of chitooligosaccharides at 1.0mg/mL reached 82.9% in 6 days after treatment.