Abstract: The control of Eichhornia crassipes Solms with glyphosate isopropylamine was evaluated by using leaf-withering index,petiole-withering index,inhibition of new roots,and fresh-weight.Residues of glyphosate isopropylamine in water was also determined.Glyphosate isopropylamine showed a high inhibition effect on new root with an LC50 f 185.54 μg·L-1.The herbicide showed a relatively low toxicity to lamina,petiole and fresh-weight of E.crassipes in the laboratory test.The LC50 on lamina,petiole,and fresh-weight reached 385.89 μg·L-1,475.82 μg·L-1,and 790.86 μg·L-1,respectively.The control of E.crassipes with glyphosate isopropylamine was also conducted in the field.Glyphosate isopropylamine at the dose of 1.91 mg·L-1 inhibited the generation of all new roots.Glyphosate isopropylamine(1.91 mg·L-1) showed 96.69% control efficiency on lamina after treatment for 20 days,while only 85.42% control efficiency was found after 40 days.The control efficiencies of the herbicide on petiole and fresh-weight were were relatively low,i.e.,52.34% and 63.18%,respectively,at the dose of 1.91 mg·L-1.Glyphosate isopropylamine applications in still and running water bodies that were 0%,60%,and 90% covered with E.crassipes were 1.37 mg·L-1,1.91 mg·L-1,and 2.73 mg·L-1,respectively.The glyphosate isopropylamine residues after the applications were all lower than 0.7 mg·L-1,the maximum limit for drinking-water set by EPA in the U.S.