Control of rheological characteristics of substrates is important in ethanol fermentation, particularly in a very high gravity (VHG) process. In this study, the synergism of cell wall degrading enzymes on rheology of cassava root mash was studied under VHG condition. The root mash exhibited a shear-thinning behavior. Crude enzyme mixture from Aspergillus aculeatus showed a dose-dependent effect on reduction of complex viscosity and storage modulus of mash. The enzyme showed strong synergism with Trichoderma reesei cellulase and Aspergillus pectinase leading to marked reduction in mash viscosity compared with individual enzymes. The optimal mixture comprising the three enzymes at a 1:1:1 ratio at 0.05mg protein/g dried solid led to a remarkable decrease of complex viscosity to 1.01 Pas at 15.79rad/s compared with 832.40 Pas of the control after incubation at 45<SUP>o</SUP>C for 2h. Synergism could be related to complementary activities of glycosyl hydrolases from different microbial sources, according to proteomic analysis. Simultaneous saccharification and fermentation of the pretreated mash by Saccharomyces cerevisiae led to a final ethanol concentration of 15.47% (w/w) corresponding to 88.14% theoretical yield. The work showed for the first time the enzymatic modification of cassava root mash rheology related to degradation of cell wall polysaccharides.