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Silicon (Si) is essential for growth of diatoms and other siliceous organisms, and plays a key role in marine ecosystems. We established a Si budget for the Bohai Sea and Yellow Sea (BSYS) on the basis of dissolved silicate (DSi) and biogenic silica (BSi) concentration measurements in two major rivers and in the water column and sediment of BSYS, and additional data from literature. The results show that BSi accounts for about 25 % of total reactive Si (DSi + BSi) in the BSYS. The budget shows that the major Si source that supports primary production in the water column of BSYS is the benthic flux, accounting for 54 % of total Si input, followed by water exchange from the East China Sea, accounting for 26 %, direct riverine input (9 %), submarine groundwater discharge (7 %), surface runoff (3 %) and atmospheric deposition (<1 %). The dominant processes that remove dissolved Si (DSi) from the water column of BSYS are primary production and subsequent BSi sedimentation, and export to East China Sea, accounting for 80 and 20 % of the Si output, respectively. About 89 % of gross BSi production is recycled in the water column over the shelf of BSYS, and 11 % settles on the sea floor. The benthic flux to the water column of the BSYS is an important DSi source, but the budget indicates that overall there is a net burial of BSi amounting to 3.6 % of total BSi production. [ABSTRACT FROM AUTHOR]