Abstract: To obtain the radioactivity baseline of marine organisms near Xiapu Nuclear Power Plant(XNPP), we collected 9 marine organism samples in 5 taxonomic groups in waters within 50 km and analyzed the natural radionuclides ²³⁸U、²³²Th、²²⁶Ra、⁴⁰K and artificial radionuclides ¹³⁷Cs、¹³⁴Cs、⁹⁰Sr、⁵⁸Co、⁶⁰Co、⁵⁴Mn、^110mAg and ⁶⁵Zn of the organisms. The radiological dose for local public and marine organisms were also assessed. The results showed that the radioactivities of ¹³⁴Cs、⁵⁸Co、⁶⁰Co、⁵⁴Mn、^110mAg and ⁶⁵Zn in all samples were lower than the detectable radioactivity limitation. The average radioactivities of ²³⁸U、²³²Th、²²⁶Ra、⁴⁰K、¹³⁷Cs and ⁹⁰Sr were respectively (0.48±0.48), (0.86±1.20), (0.27±0.34), (74.3±43.0), (0.023±0.019) and (0.242±0.167) Bq/kg, which are within the normal radioactivity background level in China. The annual effective dose for the local public due to seafood consumption is 55.1 μSv/year, of which the doses caused by ¹³⁷Cs and ⁹⁰Sr are 0.021 and 0.49 μSv/a, respectively. The radiation dose rate for marine organisms is 0.048~0.276 μSv/h. The radiation dose or dose rate for local public and marine organisms is far below the national regulation dose limit or the international recommended screening dose rate. This survey established baseline data for the marine biological radioactivity before the operation of XNPP and proposed that the key nuclides for future marine biological monitoring should include ³H, ¹⁴C, ¹³¹I and ²¹⁰Po, in addition to ¹³⁷Cs, ¹³⁴Cs, ⁹⁰Sr, ⁵⁸Co, ⁶⁰Co, ⁵⁴Mn, ^110mAg and ⁶⁵Zn.