131 I has been extensively utilized in nuclear medicine, resulting in its widespread detection in coastal algal samples due to its discharge. Therefore, it is essential to monitor 131 I in the coastal algal samples. γ-spectrometry is an expeditious method for measuring 131 I, but this method requires the pretreatment of the algal sample. The effect on 131 I in the algal sample during the oven-drying treatment is unclear. In this study, the Laminaria japonica Areschoug and Sargassum vachellianum Greville were collected at two locations and analyzed for 131 I using γ-spectrometry. Additionally, the content of iodine was measured using an Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) to clarify the effect of 131 I loss during drying treatment at different temperatures. The results demonstrated that the dried Laminaria and Sargassum samples had calculated 131 I activity concentration relative standard deviations (RSDs) of 6.34 % and 16.31 %, respectively, while the fresh samples exhibited RSDs of 11.70 % and 15.57 %. Additionally, the iodine content RSDs in the dried samples were 9.19 % for Laminaria and 10.34 % for Sargassum. Significantly, discrepancies in 131 I activity concentration between the fresh and dried Laminaria and Sargassum were 5.4 % and 10.3 %. These findings indicate that the temperature factor in drying has no effect on 131 I loss in Laminaria and Sargassum in the range of 70 °C-110 °C.