To determine the temporal variations of submarine groundwater discharge (SGD) and SGD-driven nutrients inputs, we measured the seepage rate and the nutrient concentrations of pore water/groundwater in Bangdu Bay of Jeju Island at two and three month intervals from September 2009 to September 2010. The seepage rate of groundwater ranged from 0 to 330 cm/day (average ~170 cm/day) during the five sampling periods, which increased sharply from high tide to low tide due to changes in hydraulic pressure gradient between water table in land and water sea level in the coastal ocean by the tidal cycles. The submarine inputs of groundwater were also relatively higher in summer than in winter. The nutrient fluxes from SGD were about 90~100%, 70~95%, and 65~100% of the total input (except from open ocean waters) for dissolved inorganic nitrogen (DIN), phosphorus (DIP), and silicate (DSi), respectively, potentially supporting about 0.9~33 g $carbon/m^2/day$ of new primary production in Baugdu Bay. Thus, our study suggests that SGD-driven nutrients may play an important role in the eutrophication and biological production in the coastal ocean of Jeju Island.