Recent studies have shown that peanuts in Kenya are highly contaminated with aflatoxins, however, information gaps exist on the characterization of the Aspergillus species that produce aflatoxins. Therefore, this gap necessitated the determination of the Aspergillus species producing aflatoxins in peanuts from the main growing districts of Busia and Kisii central. One hundred and two (102) peanuts samples were collected from farmers’ in each district and Aspergillus species were isolated using the dilution plate technique on modified Rose Bengal Agar. Phenotypical characterization of the identified Aspergillus flavus isolates from the samples was determined using the procedure of Mellon and Cotty. This study identified 5 Aspergillus species as contaminants in peanut analyzed. They were Aspergillus flavus L-strain, Aspergillus flavus S-strain, Aspergillus parasiticus, Aspergillus niger and Aspergillus tamari. Overall, the occurrence of Aspergillus flavus L-strain and A. flavus S-strain was significantly higher than other species identified (H = 15.55, df = 4, P = 0.004) in peanuts from the two districts. Aspergillus flavus L-strain was the most common isolate (58.8%) in peanut from Busia district while A. flavus S-strain was the most common strain (60.2%) in peanuts from Kisii central district. However, A. flavus S-strain was the most dominant species (F = 3.15, df = 25, P = 0.031) with an overall mean occurrence of 45.1%. The confirmation of occurrence of other species that produce toxins such as A. niger and A. tamarii which also produces cyclopiazonic acid, points to the need of screening peanuts for other carcinogenic mycotoxins.
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