The spatio-temporal distribution of dinoflagellate resting cysts was investigated by palynological processing to understand the harmful algal bloom (HAB) potential in the sediment of the Saemangeun area in 2003. In total, thirty-two dinoflagellate species were identified, and their concentrations were in the range of $6-1,618;cysts{cdot}g^{-1}$ (dry weight). The concentrations of resting cysts were higher in the spring (26 species, $64-1,101;cysts{cdot}g^{-1})$ and summer (30 species, $81-1,618;cysts{cdot}g^{-1})$ than in the autumn (32 species, $6-1,150;cysts{cdot}g^{-1})$ and winter (24 species, $25-728;cysts{cdot}g^{-1}).$ The composition rate of the heterotrophic dinoflagellate species to the total, which is closely related to the eutrophication process, to ranged from 6 to $29\%$ in the study area. The most dominant species was toxic Alexandrium tamarense/catenella $(25\%)$ followed by Gonyaulax scrippsea $(9\%)$ and toxic Protoceratium reticulatum $(5\%).$ Given the high abundance of the toxigenic dinoflagellate species, the Saemangeun area is considered to have the great potential for HABs in the future.