Cassava bagasse is a starch-rich lignocellulosic residue (50% of starch, by weight, on a dry basis) which is discarded daily into rivers. The enzymatic hydrolysate of cassava bagasse was used as the sole carbon source to produce fumaric acid by submerged fermentation using several Rhizopus strains. This work was developed in several steps. Six different sources of nitrogen and six different compositions of the enzymatic hydrolysate were used. An experimental design was carried out to optimize the media cultivation. The strain Rhizopus formosa MUCL 28422 was selected as the best fumaric acid producer, yielding 21.28 g/l in a media containing cassava bagasse as the sole carbon source, KNO3 as nitrogen source (C/N ratio of 168), 20 g/l of CaCO3, 10 mu g/l of biotin, 0.04 g/l of ZnSO4.7H(2)O, 0.25 g/l of MgSO4.7H(2)O, 0.15 g/l of KH2PO, and 15 ml/l of methanol.