Abstract: Based on the survey results of radioactivity levels in seawater,sediments,and marine organisms in a offshore area of Guangdong Province in 2023,this study analyzes the current status and distribution characteristics of radioactivity in the coastal waters,and compares them with radioactivity levels in different marine areas within China.The results show that the levels of U,Th,²²⁶Ra,⁹⁰Sr,¹³⁷Cs,and kalium-subtracted total beta in offshore seawater are relatively low.Among these,artificial nuclides ⁹⁰Sr and ¹³⁷Cs concentrations are far below the limits specified in the Sea Water Quality Standard (GB 3097-1997) for various seawater quality categories,and are close to the reported values in most marine areas of China.The concentrations of radionuclides U,Th,²²⁶Ra,⁹⁰Sr,and ¹³⁷Cs in sediments are similar to those reported in areas such as the Bohai Sea.The mean distribution coefficients of U,Th,and ¹³⁷Cs in sediments are lower than the IAEA-recommended values for marginal seas,whereas those of ²²⁶Ra and ⁹⁰Sr are high than the IAEA recommended values.The results of radionuclides U,Th,²²⁶Ra,⁹⁰Sr,and ¹³⁷Cs in marine organism samples from offshore waters are far below the limit values specified in the Limited Concentrations of Radioactive Substances in Foods (GB 14882-1994).Among the marine organisms,the levels of U in shellfish and oysters,Th,²²⁶Ra,and ⁹⁰Sr in blue tailed crustaceans,and ¹³⁷Cs in swordfish are relatively higher than those in other organisms.Compared to IAEA (2004) recommended values,the concentration factors (CF) were lower than the IAEA reference levels,exceptions included the CF for Th in crustaceans and molluscs,as well as the mean CF for ⁹⁰Sr in fish,crustaceans,cephalopods,and molluscs,and for ¹³⁷Cs in cephalopods,all of which exceeded the IAEA recommendations.This survey results can provide foundational data for the radioactive assessment of the offshore marine environment in Guangdong Province,supporting local radioactive pollution control,radiation safety management,and nuclear emergency preparedness.