Abstract: To evaluate the potential of several biodiesels,which had different content of fatty acid methyl ester,as substitute solvent for quizalofop-p-ethyl emulsifiable concentrate (EC),the type and content of fatty acid methyl esters in tested biodiesels were analyzed by gas chromatography,and 5% quizalofop-p-ethyl ECs were prepared with different biodiesels,respectively. The control test against gramineous weeds by the 5% quizalofop-p-ethyl ECs were carried out in greenhouse. And the surface tensions,dry durations and sediment amounts of different EC dilutions on weed leaves were investigated. The results indicated that the 5% quizalofop-p-ethyl EC could be prepared with different biodiesels and were all up to grade. The efficacy on gramineous weeds was higher than that of control EC prepared with xylene,at the dose of 2 g (a.i.)/hm2 and had no significant difference at the dose of 5 and 20 g (a.i.)/hm2. Biodiesels could not depress the surface tension of EC diluents compared with that of the xylene control,but the deposition of the former was significantly increased by 50 percent. Biodiesels could increase the penetration rate on wheat leaf. The results showed that biodiesel has the potential as substitute solvent for the preparation of quizalofop-p-ethyl EC.