Seasonal variations of the uptake and release of particulate materials by suspended oyster culture were quantitatively investigated at a floating raft (size of 200 m2) in Hiroshima Bay during October 1995 to August 1996. Samples of inflow and outflow water at the raft were analyzed for particulate matter (PM), chlorophyll a (Chl. a), and particulate organic fractions of carbon, nitrogen and phosphorus (POC, PON and PP). Sinking particles collected under the raft and ambient area (100 m away from the raft) were analyzed for sinking mass (SM) and sinking carbon, nitrogen and phosphorus (SC, SN and SP). Although the differences in C:N:P atomic ratios of particulate matter between the inflowing and outflowing waters were not significant, but materials concentration of these two waters showed significant differences. SM fluxes under the raft and the ambient area were significantly different. These results indicated the role of suspended oyster culture on materials uptake and release. In addition, the rates of uptake and release of particulate materials at the raft were found to vary with season. The uptakes of PM, Chl. a, POC, PON and PP were found in the range of 1.1-8.5 kg DW raft-1 h-1, 0.8-2.8 g raft -1 h-1, 6.7-43, 1.3-7.0 and 0.09-0.30 g atom raft-1 h-1, respectively. The uptake rates of POC and Chl. a by suspended oyster culture in Hiroshima Bay are comparable to those reported for densely populated natural oyster reefs and mussel bed in natural environments. The fluxes of SM, SC, SN and SP under the raft were found to be about 60-1,400 g DW raft-1 h-1, 1.4-12, 0.1-0.6, and 0.01-0.06 g atom raft-1 h-1, respectively. The results of the present study revealed the significant role of suspended oyster culture on the uptake of particulate materials from water column and the release of materials to the benthic environment of Hiroshima Bay.