Abstract: To explore the inhibiting effect and physiological mechanism of endophytic bacteria (Bacillus circulans) Jcxy8 isolated from tomato against Botrytis cinerea pathogen, a series of analysis were carried out including inhibitory ability analysis via of punching-poles. Results show that Jcxy8 strain inhibits mycelial growth of B. cinerea at an average inhibitory circle diameter of 35.6 mm. Inhibition rate of spore production around inhibitory circles is 66.9%. B. cinerea spores do not germinate when Jcxy8 strain culture filtrate concentration is above 40%. Microscopic observations indicate that mycelial cells around inhibitory circles fade away and twist up with vesicle-like stems or tips. Physiological analysis with spectrophotometer on tomato fruits inoculated with both Jcxy8 and B. cinerea shows increasing soluble protein content, which in is 12.7% higher than that in water, and 39.1% higher than that in fruits inoculated with B. cinerea only and activities of superoxidase (POD), superoxide dismutase (SOD), catalase (CAT) are just lower than inoculated with B. cinerea. It also suppresses the production rate of superoxide anionradicals (), implying that Jcxy8 strain significantly induces the tomato fruits’ resistance on tomato gray mould.