Abstract: Objective To study the dose distribution of ¹²⁵Ⅰ seeds in experiment phantom. Methods The dose distribution of ¹²⁵Ⅰ seeds was performed by the thermolnminescence dosimetry (TLD) method and the dose calculation formula (calculation). The radial dose of ¹²⁵Ⅰ seed was compared using measured and calculated result. Results When radioactivity of ¹²⁵Ⅰ seed was 37MBq (1.OmCi) and the radial distance is 0.5, 1.0. 1.5 and 2cm, the TLD measured and theoretically calculated result is 3.47, 0.87, 0.38, 0.21 eGy/h and 3.874, 0.952, 0.394, 0.216 eGy/h respectively. Conclusions The TLD measured and theoretically calculated result were found to good agreement. The radial dose of ¹²⁵Ⅰ seed is attenuated very apidly with radial distance.