Pesticides containing diazinon are popular in rice cultivation. Diazinon was detected in different water bodies, concentrations varying between 8–711 µg L-1 in rice field water. Snakehead fish (Channa striata) is a local species in the Vietnamese Mekong delta (VMD). The species reproduces many times a year, but mainly in the rainy season. Approximately 50% of reproduction occurs in paddy fields. After spawning, embryos or larvae float in surface water and ordinarily spend 4 days feeding from the yolk. With these ecological features, snakeheads have a high risk to insecticide exposure. Effects of diazinon based-Diazan 60EC on cholinesterase (ChE) of snakehead fish (C. striata) at early stages (larval, finished yolk, and started air-breath) were studied under laboratory conditions. Four concentrations of diazinon (2.3, 4.6, 23, and 57.5 µg L-1) and control were completely randomized, designed using 15 L glassware tank containers with 5 replications. Each replication contained 2 L of Diazinon solution and 50 fishes. Fish were sampled at 12, 24, 48, 72, and 96 hours after exposure for ChE assay. Results showed that ChE activity of snakehead at the started air breath stage was more sensitive to diazinon than at younger stages (larval, finished yolk stages). ChE was adversely inhibited at environmentally realistic concentrations at all early stages. Diazinon at a concentration of 100 times lower than the 96h-LC50 is not safe for snakehead life cycle. Further studies of the effect of enzyme P450 in the early development stages of snakehead is needed for understanding the sensitivity of early stages to diazinon