The entire local population in northwestern Tunisia uses traditional medicine to solve their health problems. In the present work, a study on the ethnobotanical and ethno ecological aspect was carried out according to a stratified and random sampling at the level of 4 stations of the region of Ouled Sedra. Ten toxic species belonging to 8 families were inventoried during this study. The results obtained showed that the elderly 53%, women 65%, illiterates 44% and herbalists 45% have a very high level of knowledge about the identified species. In addition, poisonings are generally accidental 75% and caused by the resemblance of the leaves of different plants leading to confusion. The use of these plants causes digestive disorders 28% and kidney problems 21%. The investigations carried out for the present study made it possible to collect a great deal of information on poisoning by plants. It would be desirable to use them to train professionals.