In the present work the occurrence of aflatoxin in peanut (Arachis hypogwea L.), in the region of Matão, S.P. was investigated, in three Stages, from harvest to industrialization: a) by the time the grower sells it to oil mill: Epochs I and II; b) during its storage prior to milling: Epochs III and IV and c) after oil extraction (peanut flour) : Epochs V and VI. In each stage two collections, of 10 samples each, were made in a total of 40 samples of peanuts and 20 samples of peaunt flour. From the results the following conclusions could be drawn; a) the majority of the samples, representing 85%, was toxic; b) the toxicity level of the samples, in terms of aflatoxin B1, grew from Epoch I to Epoch VI, presenting the average values of 0,06 ppm in the first and 1,22 ppm in the last one. The total mean value reached 0,44 ppm; c) good drying practices and proper storage can definitely help to maintain peanuts in a low level of aflatoxin and even prevent the occurrence of the toxin; d) the aflatoxin is already present in peanuts when growers take it to the oil mill.