Abstract: Effect of two kinds of conditioning methods, biological acidification and acid treatment, on sludge dewaterability was studied. Experimental results showed that, the dewaterability and stability of biological acidification conditioning were superior to chemical acidification. With 10% inoculation of Acidithiobacillus ferrooxidans bacteria liquid，the dewaterability had been impoved greatest by 49.7% compared with the original sludge, while acid treatment of initial pH 3.2 had just been impoved by 30.8%. The sludge systems’ pH varaiation compared during conditioning process, it was found that when the quantity of inoculation was certain, biological conditioning method can maintain the acidic environment conductive to dehydration longer. By electron microscope scanning (SEM), intuitively the sludge shape of bioleaching treatment was uniform, large porosity, soft texture, and bacteria strain were seen. Infrared spectrum results showed that, Acidithiobacillus ferrooxidans decomposed protein of extracellular polymeric substances (EPS) through enzyme action, thus improving sludge dewatering performance.