Abstract: In order to isolate and screen plant endophytes capable of degrading chlorpyrifos, horseweed herb(Conyza canadensis(L.) Cronq) collected near the waste pool of a pesticide factory was used as target plant. After surface sterilization, the plant tissues were triturated to obtain plant juice. The plant edophytes were screended by plating the plant juice on minimal salts media(MSM) modified with chlorpyrifos as the sole carbon. After 5 times successive screening, a strain named as XFP-gy capable of degrading chlorpyrifos was isolated. It was identified as Cronobacter sp. based on its physiological-biochemical characteristics and 16SrDNA sequence. The growth of strain XFP-gy reached the maximum at the 6th day in liquid MSM with initial chlorpyrifos concentration of 20 mg/L, and 77.28% chlorpyrifos was degraded after 9 days' inoculation. The degradation rate could be enhanced up to 98.0% at the 5th day by adding beef extract and peptone in MSM. The optimal temperature for XFP-gy degrading chlorpyrifos is 30 ℃, and the optimal pH value is 7.0. Under optimal incubation condition, the chlorpyrifos degradation efficiency increased with the increasing initial bacterium inoculum amount, and the decreasing substrate(chlorpyrifos) concentration in the media. No chlorpyrifos was detected at the 9th day when the initial inoculum of XFP-gy was 2% and concentration of chlorpyrifos was 10 mg/L.