Dehydrated sludge with two concentrations of total suspended solids (high: 50 g/L TSS; low: 20 g/L TSS) were studied for 20 d to investigate the effects of anaerobic fermentation on sludge properties. The results showed that the soluble chemical oxygen demand (SCOD) of high-concentration sludge was 16.53 g/L, much higher than that from the low one. The SCOD/total nitrogen ratio of high-concentration sludge varied from 8 to 14.29 g/g, indicating that the sludge could serve as a carbon source for biological denitrification. High-concentration sludge showed a short-chain fatty acid yield of 11.29 g COD/L, much higher than that from low-concentration sludge. The specific resistance of the sludge to filtration (SRF) increased with fermentation time. The quantity of low-speed centrifugation substances (LSCS) was the main factor that influenced the reduction of dehydration. The correlation coefficient between the SRF and protein content in the LSCS layer was significantly positive.