ABSTRACT: In order to enhance the oxygen production in anoxic bottom water using light, the bottom water and sediment collected in different seasons from a coastal area were incubated under irradiance treatments of 7 and 15 µE/m2 per s by halogen lamp provided through an optical fiber. The dissolved oxygen (DO) concentrations increased from 3.6 mg/L to 7.1 mg/L in the 15 µE/m2 per s irradiance treatment, while in the dark control the DO concentrations decreased to 1.1 mg/L in June. Along with the oxygen increase, chlorophyll a concentration increased from 0.24 µg/L to 1.35 µg/L while inorganic nitrogen and phosphorus decreased. These results indicate that low-intensity light is effective in stimulating photosynthesis of coastal bottom water and for net production of DO, especially in summer. It is a promising way to improve the anoxic bottom environment.