The aim of this study was to measure aflatoxin B1 in granola sold in stores in the city of Teresina, Piaui. Sixty samples of granola sold in four supermarkets were used. The mycological evaluation was carried out immediately, and then the samples were stored at -4°C, for later analysis of aflatoxin B1. Thirty-one strains of Aspergillus flavus were isolated. Two strains demonstrated capacity for aflatoxin production with aflatoxin B1 concentration of 2.30 and 3.90 µg/g. Sixty percent of samples tested positive for aflatoxin. Granolas may have different levels of aflatoxin B1, a risk for the consumer. Therefore, there must be better control of the quality of raw materials used to make granola, because they may be the source of contamination by aflatoxins. Key words: Aspergillus flavus, cereals, fungi, grains, mycotoxins.