Acute toxicity and effects of insecticide chlorpyrifos ethyl on cholinesterase (ChE) enzyme in fingerling snakehead fish (Channa striata) have been tested in Can Tho University. Median lethal concentration (LC50) has been carried out under the static and non-renewed water system. Effects this insecticide on ChE activity in the species were done by exposing fishes into sub-acute concentrations and then removing them into clean-water for ChE recovery monitoring. The result has shown that LC50-96 of Chlorpyrifos Ethyl for big fingerling snakehead fishes is 27.1 ppb. The ChE activity in the brain of snakehead fish is very sensitive with this pesticide; the significant inhibition has been seen at the concentration of 1.36 ppb. The highest ChE inhibition has been seen after 48 to 60 hours of exposure. ChE can have quick recovery after 2 days living in clean water. The study has shown that Chlorpyrifos Ethyl is very toxic to snakehead fishes. The field studies on this species and Chlorpyrifos Ethyl are recommended for fully understanding the impacts of using this pesticide in rice cultivation in the Mekong river delta on snakehead fishes in nature.