This study was carried out to investigate the charateristics of environmental factors and the species compositions of phytoplanktons and periphytons in order to analyze the marine ecosystem (DOK1-3) with freshwater (Mul) in the coast of Dokdo. Mean values of conductivity (TSD) (44.3 mS cm?1), total dissolved solids (30.9 mg L?1), salinity (31.8 psu), total suspended solids (39.2 mg L?1), and ash-free dry matter (AFDM) (8.8 mg L?1) were higher in DOK1- 3 than those in Mul (3.2 mS cm?1, 2.3 mg L?1, 1.9 psu, 2.8 mg L?1 and 2.8 mg L?1, espectively), while mean amounts of soluble reactive phosphorus (SRP) (7.5 μg P L?1) and soluble reactive silicon (SRS) (0.1 μg Si L?1) were significantly lower in DOK1-3 than those in Mul (117.3 μg P L?1 and 4,105 μg Si L?1, respectively). The phytoplanktons was a total of 59 species in Dokdo, which were composed of 1 species (1.7%) for Chrysophyceae, 43 species (72.9%) for Bacillariophyceae and 15 species (25.4%) for Dinophyceae. The biomass (Chl-a, phaeopigment and AFDM) of epilithic algae (ELA), epizooic algae (EZA) and epiphytic algae (EPA) were varied with the kinds of substrates (EPA > ELA > EZA) in the whole stations. Water environments was comparatively clean in the coast of Dokdo as comparing with those of the land. However, the monitoring of marine ecosystem in the Dokdo should be continued for species conservation according to the global warming by the climatic change.