Abstract: The difference in bioactivity , poisoning symptom and effect on content of glutamic acid(Glu) and γ-aminobutyric acid(GABA) in larva of armyworm between abamectin and fipronil were determined and compared. The result showed that the LD50 of abamectin and fipronil to the 5th instar larvae of armyworm were 0.072 and 8.920 μg/larva respectively. Abamectin caused insects tested paralysis and death directly, but the poisoning symptom of fipronil could be divided into four stages, exciting, convulsive, faint (prostrate) and dead. They both caused abnormal metabolism of Glu and GABA in insects tested. Glu content in armyworms treated by abamectin was increased 1.8-fold as much as in check , but GABA content was decreased to 71.3% of check. Fipronil could induce Glu content in insects tested increasing 1.2-fold in convulsion stage as much as in check, but same as check in paralysis stage; in paralysis stage, the GABA content was decreased to 76.7% of check.