Abstract: There are few reports on the evaluation of uncertainty for the tritium activity concentration in biological sample. In order to improve the measurement reliability and accuracy of the results for radionuclide determination in aquatic products, in this study, a mathematical model was used to evaluate the uncertainty of the tritium activity concentration in aquatic products. The liquid scintillation counter was used to measure the concentration of tritium activity in aquatic products and an analysis was conducted on the uncertainties in the measurement process, including sample counting, detection efficiency, the recovery rate of oxidation combustion device, sample weighing, the volume of measured water sample and other factors. For measured codfish（Gadus）, salmon（Oncorhynchus）, and king crab（Paralithodes camtschaticus） samples, the results show that the uncertainties introduced by the sample counting and detection efficiency are the main factors. The activity concentration of the radionuclide tritium in the codfish, salmon, and king crab samples are（ 10.6±0.95 ）Bq/kg,（ 6.0±0.72） Bq/kg and （10.4±1.01） Bq/kg respectively, with the inclusion factor k=2. This evaluation can serve as a reference for the uncertainty evaluation of the tritium activity concentration in aquatic products.