At present, fish consumption rate is growing due to health consciousness. High protein and high omega-3 can be obtained, especially from marine fish species. However, not only essential nutrients but also toxic elements can exist in fish. To evaluate food safety, Neutron Activation Analysis (NAA) was performed to determine the toxic elements in the edible parts of fish samples. NAA is a multi-element analysis technique with high accuracy and precision using the interactions of neutron radiation. In this work, ten popular fish samples were collected from a supermarket in Bangkok. Then, fish samples were cut and freeze dried at -60°C for 72 hours, and finally weighted. The Thai Research Reactor TRR-1/M1, of which the flux is 10¹¹-10¹² n/cm²s, was employed as the neutron source. The standard reference materials: bovine mussel powder and oyster tissue, were used for comparison. The essential and toxic element contents were successfully investigated by NAA technique. A total of 13 elements are detected from the edible parts of the fish samples. The results show that the toxic elements, As, Hg and Cd were presented in fish. The method was validated by analyzing the standard reference materials, the results were within the acceptable range of certified value. In addition, the evaluation of the detection limits for fish sample analysis was carried out. Finally, to evaluate the food safety, the permitted level of toxic element in food from Ministry of Public Health was then compared.