This thesis investigates the variation of the chlorophyll-a concentration near Dongsha Atoll derived from MODIS Aqua and Terra satellite images, and their relationship to physical environments including sea surface temperature, CTD water qualities, tides, currents and surface winds for the period 2005 to 2008. The results revealed that the seasonal variation of chlorophyll-a concentration was higher in the winter than in the summer, and had inverse relationship with sea surface temperature. The increased chlorophyll-a concentration was due to entrainment of lower layer cold water with high nutrient. The upwelling water was induced by mixing of surface wind and internal wave shoaling. When the internal waves propagated westward to the Dongsha Atoll, the bottom topography and coastline oriented the cold deep water surged up slope to the northeastern corner of the Atoll, which produced high chlorophyll-a concentration a few days after. The comparison of MODIS images and CTD data revealed that the chlorophyll-a concentration didn¡¦t increase immediately after the passage of internal waves.