ABSTRACT: The effect of open and controlled fermentation on the proximate composition, some mineral elements, antinutritional factors and flatulence- causing oligosaccharides of a domesticated bean (Vigna unguiculata) was studied. The open fermentation was carried out using the microorganisms present in the atmosphere, while the controlled fermentation was carried out using Aspergillus niger as a starter. The two types of fermentation brought about more than 20% increase in the protein content. The lipids, carbohydrates, crude fibre and ash content were all reduced by less than 75% by both processing techniques, except the level of moisture content which increased in controlled fermentation. Apart from calcium, the other elements (Fe, Na, Mg, Zn, and K) suffered from less than 90% reduction by the two types of fermentation. The phytate, tannin, alkaloids, hydrogen cyanide, lectins, trypsin inhibitors and oxalate content all had more than 20% reduction by the two types of fermentation. The percentages of reduction due to controlled fermentation were higher than those of open fermentation in the eight antinutrients studied. Fermentation is, therefore, an efficient method for detoxifying the antinutrients in the cultivated beans studied in this work.