| Herbicide becomes more commonly used in Vietnamese agriculture nowadays. Statastic data indicated that the quantity of herbicide used in 2010 is 20.342 thousand tons, taking by 28,4% of the total pesticide and increased by 3,12 l time compared to the data of 2000. Beside positive contribution on reducing labor cost of weed control, herbicide may cause some negative effects on agriculture environment including aquatic animal, soil micro-organisms and benefit insects. However, there has not been systematic researches on the above issue. The research findings in this paper initially showed that all of 8 herbicide activities commonly used in water rice in Vietnam currently caused slightly to fairly effects on population of 4 target benefit insects including total spider, Lycosa pseudoannulat and total beetle and Micrapis discolor. The density of those population is most sharply decreased at 14 days after spraying and recovered at 35 days. There has been no long term effect of herbicide in the next crop season observed.