Spatial distribution and biomass of commercial shellfish were investigated in the Saemangeum tidal flat on the west coast of Korea during August 1999. Thirteen species of shellifsh were collected. Major dominant species of the study area were Umbonium thomasi with a density of $6.7;ind.{cdot}m^{-2};(38.2\%)$, Mactra veneriformis with $6.6;ind.{cdot}m^{-2};(37.4\%)$ and Reticunassa festiva with $1.3;ind.{cdot}m^{-2};(7.2\%)$. Commercially important species such as M. veneriformis ($90.7;ind.{cdot}m^{-2};69.3\%$), M. lusoria ($15.6;ind.{cdot}m^{-2};11.9\%)$), C. sinensis ($8.7;ind.{cdot}m^{-2};6.7\%)$) were dominant in total weight. Most of the shellfish were distributed between the mid-littoral and sub-littoral zones, but C. sinensis and L. flexuosa were distributed mainly in the polluted areas of the supra-littoral zone. The spatial distribution pattern of each shellifsh species generally resembles the Mangyeong and Dongjin estuary. Biomass of commercially important species, M. veneriformis, M. lusoria, C. sinensis and Ruditapes philippinarum in the tidal flat (ca. 850 ha) was estimated to be 774, 135, 67 and 10 tons, respectively.