We have measured the entomological impact of insecticide treated nets on malaria transmission at Ganvie, a village in the coastal and lagoon area of Benin. The nets we have impregnated belong to the population of this village. Men and women of Ganvie used the nets everyday against nuisance biting. Then, the nets we have impregnated are not experimental nets introduced in the village. We have treated 3,230 nets, that means 79% of the nets of this village which counts 20,000 inhabitants. After treating the nets, the inoculation rate due to Anopheles gambiae s.s. and A. melas has decreased from 11 to 4.6 infected bites per man/year, that represents 58.5% of reduction of malaria transmission. We have also observed that the parturity rate of anopheles has decreased from 45.3 to 38.8%. We are sure that the entomological performances due to the impregnation will increase more if the inhabitants of Ganvie change their behaviours. They must reduce the frequency of impregnated net wash and repair the teared nets.