²²⁶Ra and ²²⁸Ra analysis were carried out at the representative station of Masan Bay from May to August, 1999. The high activities of ²²⁶Ra and ²²⁸Ra in the surface water were appeared in rainy season (August, 1). However, there is no significant variation in concentrations in the other season. A high negative linear correlation between ²²⁶Ra activities and salinity in the surface water suggests that ²²⁶Ra activity in the surface water was controlled by simple mixing between the two end-members low salinity high ²²⁶Ra activity water of inner Bay and a high salinity low ²²⁶Ra activity water of the continental shelf water out of Bay. ²²⁶Ra activities below the surface mixed layer were higher than those of expected level from the ²²⁶Ra versus salinity. And also ²²⁸Ra/²²⁶Ra ratios in the bottom water were lower compared to those in surface water due to the presence of potential source of ²²⁶Ra below the surface mixed layer. However, it is known that ²²⁸Ra compared to ²²⁶Ra is enriched in bottom sediments and pure water. Therefore, the most probable sources for low ²²⁸Ra/²²⁶Ra activity ration is submarine ground water discharge. Further studies are required to quantify the various sources of ²²⁶Ra and ²²⁸Ra and their relative contributions.