Abstract: Monosulfuron-ester is a patented novel sulfonylurea herbicide with ultra-low dosage of application.In order to improve its environmental property,sodium monosulfuron-ester was synthesized by reaction of monosulfuron-ester and sodium hydroxide in water at room temperature;the structure was comfirmed by 1H NMR,IR,MS and elemental analysis.Its herbicidal activity was compared with monosulfuron-ester by greenhouse bioassay using Digitaria ciliaris,Echinochloa crusgalli,Amaranthus retroflexus and Chenopodium aldum which indicated that the two compounds have the same level of herbicidal activity.