The antioxidant and antigenotoxic effects of solid state fermented cassava (Manihot esculenta Crantz) using Rhizopus oligosporus were investigated. Solid state fermentation was carried out for 72 h at room temperature under acidic and basic conditions. Total phenolic content was significantly (p<0.05) higher in fermented peeled and unpeeled cassava at pH 7 and 5 when compared with unfermented. Similarly, the total flavonoid contents of fermented peeled and unpeeled cassava at pH 4 and 7 were significantly (p<0.05) higher than in unfermented. Allium cepa assay was used to assess the antigenotoxic effects of unfermented and fermented peeled and unpeeled cassava. The fermented extracts did not induce chromosomal type aberrations in the treated cells. The present study thus showed that R. oligosporus has the ability to breakdown cassava and considerably increase the antioxidant properties in peeled and unpeeled fermented cassava, which may serve as natural antioxidants in industrial broiler chickens.