Abstract: Twenty-two sludge samples were collected from 13 cities in the Yangtze River Delta region, and were used to investigate the concentration, size, speciation distribution, and bioavailability of silver (Ag) in sewage sludge. Meanwhile, the leaching toxicity and human health risks of Ag in sewage sludge were evaluated by the leaching toxicity procedure for solid waste and the health risk evaluation method recommended by the US Environmental Protection Agency. The results showed that the Ag concentration in varied sludge was significantly different (0.08-721 mg/kg), and the average Ag concentration in different types of sludge exhibited an order of industrial sludge (101 mg/kg) > mixed sludge (1.89 mg/kg) > municipal sludge (0.99 mg/kg). The results of single particle inductively coupled plasma mass spectrometry (spICP-MS) indicated that Ag-containing nanoparticles existed in different types of sludge and the size fell in the range of 17.7-19.0 nm. The analysis results of the occurrence forms indicated that the proportions of weakly acidic extracted Ag were higher in two types of industrial sludge with acidic or low organic matter content (S17 and S22, Nanjing), which were 60.0% and 15.6%, respectively. However, Ag in the remaining 20 types of sludge was mainly found in stable fractions (residual fraction and iron manganese oxidation fraction), indicating that the migration ability of Ag in most of the sludge (90.9%) in this region was relatively low. The EDTA extraction efficiency results indicated that, except for one acidic industrial sludge (S17, Nanjing), the bioavailability of Ag in the other 21 types of sludge was relatively low. The results of leaching toxicity indicated that except for one industrial sludge with low organic matter content (S22, Nanjing), whose Ag had a high leaching toxicity risk, the leaching toxicity risk of Ag in other sludge was relatively low. The results of the human health risk assessment indicated that Ag in the sludge from the Yangtze River Delta region did not pose a significant non-carcinogenic risk to adults and children. The above results suggest that from the perspective of Ag, the environmental risks of municipal and mixed sludge in the Yangtze River Delta region are relatively low, except for some industrial sludge.