Mercury and methylmercury concentrations were measured in 225 marine fish samples purchased from retail markets in 5 major Korean cities in 2005. The results showed that the concentrations of mercury and methylmercury ranged from 0.006-0.455 (mean=$0.054{pm}0.025$) mg/kg and 0.004-0.120 (mean=$0.021{pm}0.008$) mg/kg, respectively, in fish caught from the coastal waters of the Korean Peninsula. The concentrations in deep-sea fish including tuna ranged from 0.066-2.315 (mean=$0.095{pm}0.640$) mg/kg for mercury and 0.027-0.897 (mean=$0.281{pm}0.182$) mg/kg for methylmercury. The estimated weekly intakes (EWIs) of mercury and methylmercury reached 3.92 and 4.70% of the provisional tolerable weekly intakes (PTWI), respectively. Consequently, the levels of mercury and methylmercury in marine fish from current retail markets do not pose any significant health risks for Koreans.