The citric acid sludge was conditioned biologically with the separated filamentous fungi Aspergillus niger SS5 before dewatering in the paper. Results showed that fungi concentration and conditioning time both had strong effects on the sludge dewaterability, and the performance of sludge dewatering and settlement were improved significantly. Combined with the analysis of Zeta, particle distribution and bound water concentration, it was observed that negative charge of sludge decreased accompanied by obviously increasing particle size. The concentration of bound water had a reduction of approximate 40% to the control sample without fungi conditioning. Meanwhile, the concentrations of COD in supernatant and protein and polysaccharide in each EPS layer were all decreasing during the sludge conditioning with fungi. There were significant correlations between protein degradation in EPS and bound water content, D₅₀ and Zeta potential, which indicated it was the important factor affecting citric acid sludge dewaterability. Due to the large pH buffering capacity of citric acid sludge, the great pH change was not observed during the decomposition of organic matter in sludge. 71.98% water content of the dewatered sludge cake was obtained with 20mL/g DS Aspergillus niger SS5 conditioning for 3d without chemical additives. It should make for further resource utilization of these food fermentation sludge as citric acid sludge.