Suspended particulate matter (SPM) was collected to measure the particulate biogenic (PBSi) and lithogenic (LSi) silica in the Changjiang Estuary and its adjacent sea.In addition, the mesocosm experiments were carried out to discuss the distribution and variation of PBSi and relationships between PBSi and other environmental factors. Average Concentrations of PBSi and LSi are 1.12μmol/L and 39.74μmol/L, respectively.The content of LSi is much higher than that in the other regions of the world,but the concentration of PBSi is in middle level.Both the content of PBSi and LSi showed higher values in the coastal areas than offshore areas,due to the huge freshwater discharge with abundant sediment loads from the Changjing river.In addition,both the values of PBSi and LSi in bottom waters are higher than those in upper waters because of the resuspended SPM.PBSi is closely related with silicate and SPM,but the Prorocentrum donghaiense was bloom in the investigation periods and only a small amount of PBSi was bound to identifiable diatom cells,so the distribution of chla was different from that of PBSi.During the mesocosm experiments, the biomass of diatoms increased with nutrients addition,followed by the higher concentration of PBSi, but the concentrations of nutrients did not affect the LSi level.