We used an oxygen microsensor for high-resolution measurements of pore water oxygen concentration in semiclosed coastal bays of the South Sea of Korea during summer. The oxygen penetration depths ranged from 0.60 to 3.65 mm. Oxygen consumption rates were estimated to be 9.1 to 59 mmol $m^{-2}d^{-1}$ (average: 22.8 mmol $m^{-2}d^{-1}$). At the sediment water interface, the oxidation rates of organic carbon were estimated to be 84-545 mg $Cm^{-2}d^{-1}$ (average: 211 mg $Cm^{-2}d^{-1}$). Approximately 38% (~211 mg $Cm^{-2}d^{-1}$) of pelagic primary production was regenerated in the surface sediment, indicating the tight benthic pelagic coupling in the coastal sea of the South Sea of Korea.