The distribution of dimethylsulfide (DMS) was studied in surface seawater and vertical profiles at nineteen stations in the Nansha Islands sea area of the South China Sea. The concentrations of DMS in surface-layer (0-1 m) seawater vary from 64 to 140 ng S/L with high values found in the productive regions, in agreement with the horizontal distribution of chlorophyll a. The vertical profiles of DMS show a single peak shape with maximum concentrations occurring at depths between 30-75 m. The DMS concentrations are correlated with chlorophyll a levels both in the upper 20 m of seawater as well as in vertical profiles. A clear diel variation in DMS concentration is observed at the 50-m water layer at a fixed station with the highest DMS concentration found in the late afternoon. The DMS concentrations are associated with environmental factors such as seawater temperature, dissolved O2 and nutrient contents. Although DMS is correlated to chlorophyll a, the phytoplankton species is a major factor responsible for the obviously higher DMS concentration than expected from the phytoplankton biomass in this sea area. The sea-to-air flux of DMS from this sea area is calculated to be 7.6 µmol m-2 d-1.