Realistic temperatures (24±0.3, 30±0.3, and 34±0.2oC) and dissolved oxygen (DO) levels (1.8±0.2, 6.5±0.7 mg L-1) that can be found in rice fields of the Mekong River Delta were manipulated in a full factorial block design experiments in the laboratory to determine the effects of these parameters on brain cholinesterase activity of juvenile snakehead fish (Channa striata) exposed to realistic concentration of quinalphos (2.45 µg L-1). The results show brain cholinesterase inhibition increases significantly with temperature, while no such impact was seen with DO. These parameters did not affect the brain cholinesterase activity in unexposed fish. With the trend of global warming and extreme fluctuation of weather, current rice farming practices in the Mekong River Delta would cause more health risk for snakehead fish in ricefield habitat. Field investigation is recommended to confirm the prediction