We determined the influence of Sargassum beds on the water quality in Gamak Bay, Korea. Water temperature and salinity range from 3.3 to $23.4^{circ}C$ and from 29.6 to 33.7 psu, respectively. Dissolved oxygen was 10.45 mg L-1 in the Sargassum bed and 9.23 mg L-1 in the control. Chlorophyll-a was $3.90{mu}g;L^{-1}$ in the Sargassum bed and 2.21${mu}g ;L^{-1}$ in the control. Chemical oxygen demand were 1.14${mu}g;L^{-1}$ in the Sargassum bed and 1.43${mu}g;L^{-1}$ in the control. Total nitrogen were 0.038${mu}g;L^{-1}$ in the Sargassum bed and 0.067${mu}g ;L^{-1}$ in the control. Total phosphorus were 0.043${mu}g ;L^{-1}$ in the Sargassum bed and 0.072${mu}g ;L^{-1}$ in the control. Multivariate statistical analysis was used to analyze data. Water temperature was highly positively correlated with DO (p<0.01). T-N was highly positively correlated with T-P (p<0.01).