Abstract: A new formulation,abamectin microemulsion,was prepared using organosilicon co-formulant (Silwet 408).Technical specification,physical-chemical characteristics and biological efficacy of the new formulation was compared with common microemulsion or emulsifiable concentrate(EC) of abamectin.The quality specification of the new formulation not only met the quality standard of common microemulsion,but also saved 70% solvent and 7% surfactant by optimizing the solvent system.The test of thermal stability showed that the decomposed ratio of abamectin was 1.12% ,and that of Silwet 408 was below 1.0% ,after being stored at (54±2) ℃ for 14 days.The diluted solution of the new preparation showed decreased surface tension by 10 mN/m, reduced contact angle by more than 10°,increased spread area by 5 mm2,and dropped wetting time to less than 1 min comparing with common microemulsion or emulsifiable concentrate of abamectin.Field control efficacy of microemulusions containing Silwet 408 against the pest at application rate of 7.2 g (a.i.)/hm2,was 96.8%,while that of EC was only 94.5%.When using low volume spray at application rate of 3.6 g (a.i.)/hm2,the field control efficacy was 88.4%,higher than that of high volume sprayat the same application rate,which was 82.7%.The trial results suggested that the physical-chemical characteristics and control efficacy of microemulsions containing Silwet 408 was superior to that of common microemulsion or emulsifiable concentrate of abamectin,and it was more suitable to be applied by low volume spray.