Traditionally, cassava (Manihot esculenta Crantz) is transformed by fermentation in water (retting) or in the open air (dry fermentation) in the DRC. In the east of the country (North Kivu), dry fermentation is the main technique for processing cassava for its detoxification and conservation. The Congolese farmers ferment the cassava to the open air using a preselected microferment contained in the scrapings of the fermented cassava previously called "MUSIYIRO". These fermentations are spontaneously directed by the microorganisms of the uncontrolled autochthonous flora. Unfortunately, toxinogenic molds are often more active in the fermentation process during which they also produce aflatoxins. This study was undertaken to help prevent the production of aflatoxins in cassava during this process. To do this, we substituted the traditional ferment with a strain of Rhizopus oryzae used as starter (microferment). Six successive replications, in controlled fermentation and uncontrolled fermentation, in a peasant environment (Beni, North Kivu) and fermentation directed by the strain of R. oryzae were carried out. Aflatoxins were then dosed in both groups of cassava flours. The results of the assay revealed an absence of aflatoxins in cassava fermented by scrapings from fermentation led by R. oryzea, while the non-directed fermentation controls were all contaminated with aflatoxins. These results show that it is possible to prevent the production of aflatoxins in cassava during fermentation when an aflatoxin-inhibiting microbial biomass is used which can progressively invade and colonize the fermentation site and thereby control the fermentation activities of cassava.