The purpose of this study was to investigate the concentrations and spatial distributions of mercury (Hg) species in seawater (including dissolved, particle, and total Hg) and sediment (including total and methyl Hg) of the Xiamen western sea area adjacent to a coal-fired power plant. The influence of the wastewater discharged from the seawater desulphurization (De-SO2) system of the power plant is discussed. Concentration of the three species of mercury in seawater from 18 sampling sites varied: dissolved ranged from 0.70 to 4.65 ng/L (mean 1.47 ng/L; median 1.12 ng/L); particulate ranged from not detected to 90.52 ng/L (mean 10.47 ng/L; median 1.26 ng/L); and total was 1.51 to 92.88 ng/L (mean 11.94 ng/L; median 2.84 ng/L). High concentrations of total Hg and particulate Hg, more than 70 ng/L, were observed in the area adjacent to the outfalls of the power plant. The Hg from the waste seawater of the power plant might be re-emitted to the atmosphere because it exists in seawater mainly in particulate attached form. The sediment total Hg concentrations ranged from 0.055 to 0.201 microg/g, with a mean of 0.126 microg/g and a median of 0.125 microg/g. Low methyl Hg concentrations in the sediment were observed in the study area, ranging from 0.017 to 0.256 ng/g as Hg, with a mean of 0.087 ng/g and a median of 0.081 ng/g. The ratios of methyl Hg to total Hg in the sediment were low, with a mean and median of 0.069%. Both total and methyl Hg were significantly linked to the sediment organic carbon (SOC).