Abstract: A 36% emulsion oil of Illoxan is currently an ideal herbacide for sugar beet, both domestically andabroad. The purpose of studying the degradation and residue dynamics under field condition was to providenecessary residue data of this herbacide for its reglstered from and at the same time to make a scientificbasis for its "standard of safe usage" . From 1984 to 1985, the authors used three dosages for Illoxan onexperimental fields on Zhejiang province, Beijing municipality and Helongjiang province at: 83 ml/mu, 125ml/mu and 16T ml/mu. After 92-106 days of application, no residue of Illoxan could be detected in thebeet tubers, nor in the soil.It was suggested that the interval for safe application of Illoxan should be 106days, the permissible residual amount eas 0.1 mg/kg and the application rate should be one per growingseason at the rate of 83 ml/mu.