Abstract: The IC50 and IC10 of metsulfuron-methyl and its mixture with bensul furon-methyl, cinosulfuron, pyrazosulfuron-ethyl respectively to rice seedling of single-leaf were evaluated. Results showed that the security sequence i s bensulfuron-methyl＞pyrazosulfuron-ethyl＞cinosulfuron＞metsulfuron-methyl when used alone. Bensulfuron-methyl increased the security when mixed with mets ulfuron-methyl, but pyrazosulfuron-ethyl, when mixed with metsulfuron-met hy l decreased the security in some consistency. Cinosulfuron decreased the securit y more severely when mixed with metsulfuron-methyl.