: In tannery industries, Cr is used for tanning animal hides. Three valence chromium reacts in specific conditions with +3 existing organic compounds and manganese ions to change to hexavalent chromium which is considered hazardous for human health. Aspergillus oryzae grew in different dilutions (10-90%) of tanning house effluent (concentration of Cr =120-1080 +3 mg/L). The maximum chromium removal rate, (48.2%), was observed at pH= 3.3, Cr concentration=240 mg/L and size of +3 inoculum=0.12% (dry weight). Effects of various factors such as pH, temperature, shaking velocity and nutrients were also investigated. At optimum conditions (pH=5; temperature=30 C, shaking velocity= 150 rpm and nitrogen source of o dihydrogen ammonium phosphate concentration=0.3%), biomass growth and chromium removal rate were found to be 0.45% of dry weight and 99.8%, respectively. Statistical studies on factors such as pH, temperature, shaking velocity, type and concentration of nutrients on the “biomass growth” and “residual chromium”, showed that all the factors had significant effects