This study was aimed at elaborating prevention behaviours from pesticide poisoning among farmers in Amphur Nonsa-aad, Udonthani province. The study was cet in 6 villages from which 293 farmers having used organophosphate and organocarbamate pesticides were recruited. Of these users, 100 used only organophosphates, 14 used only organocarbamate, 179 used both. Survey of preference of brands used was found that Decarbam 50 and Furadan 3% were the most popular pesticides(46.79% and 45.39% respectively). Others were Folidon E 605(27.3%), Spato(17.41%), Anthracil 60(12.29%). Vegetables most frequently used of pesticides were Tang-ran-yai(Curcumis sativas)(74.74%) and Tang-tai(Curcumis melo)(74.74%). Others were long bean(22.87%), waterrmelon(19.8%), chilli(10.92%). Blood cholinesterase in farmers was also tested using ‘reactive paper’ before and after spraying pesticides for 2 – 4 hours. Prevention behavious from pesticide poisoning of farmers were categorised in this study into 3 stages of practice, i.e., preparation, spraying and after spraying. Same data were collected using 2 methods, i.e., from in-depth interview and a direct observation. From interviewing, inappropriate practices among 293 farmers in the preparation stage were found in mixing of pesticides(2%), gloves wearing(48.1%), masks wearing(36.2%). After spraying, inappropriate practices were found such as equipment used(0.7%), clothing(11.9%), gloves wearing(35.2%), shoes wearing(39.9%), walking direction according to wind(44.4%), eating and drinking food or smoking(24.4%). After spraying, inappropriate practices were found. These were bathing(20.8%) and clothes changing(7.8%). From direct observation, inappropriate practices among 34 users in the preparation stage were found in gloves wearing(67.6%) and mask wearing(52.9%). During spraying stage, inappropriate practices were found about clothing(11.8%), gloves wearing(61.8%), mask wearing(50.0%), shoes wearing(44.1%), walk direction according to wind(38.2%), eating and drinking food or smoking(23.5%). After spraying, inappropriate practices were found in bathing(41.2%), clothes changing(8.8%). Deviation in percentage found between the 2 methods may have been due to practicing from different frame and2or that some farmers gave answers for an interview different from the real practices. Blood cholinesterases found before spraying period from 239 farmers were in ‘in-risk’ and ‘not-safe’ levels for 41.0%. After spraying pesticides for 2 – 4 hours, blood cholinesterases of 43 users were ‘in-risk’ and ‘not-safe’ levels for 53.49%. When the blood cholinesterases were compared within the same users of 24 farmers, 41.6% was found in ‘in-risk’ and ‘not-safe’ levels before spraying period and the number was increasing to be 58.4% after spraying. Symptoms after spraying were described by farmers in orderly. These were headache(43.3%), nausea2vomiting(11.3%), dyspnea(8.2%), sweating(6.8%), tremor(6.5%), saliva increasing(6.5%) and moth dryness(5.1%). The study concluded that farmers had inappropriate prevention behaviours from pesticide poisoning in all the three stages of practice, i.e., in preparation, spraying and after spraying pesticides. The decrease in blood cholinesterases after spraying pesticides 2 – 4 hours go along with these inappropriate practices.