Abstract: The thallium (Tl) isotope system can be utilized to track various geological processes, but the current sample digestion and ion exchange methods used for Tl isotope analysis take a long time. To improve the efficiency of chemical pretreatment of samples for Tl isotope analysis, the samples were decomposed by the microwave digestion method. In the mixed acid system of 2mL HNO₃, 2mL HF and 0.5mL HClO₄, 0.2g of GBW07406 could be completely dissolved by selecting the digestion procedure. The slurry was then loaded on AG1-X8 resin, followed by eluting with 2mL 2mol/L HNO₃-1% Br₂ for 6 times, 2mL H₂O for 1 time, and 2mL 0.1mol/L HCl-6% SO₂ for 5 times (Tl collection). The amount of Fe³⁺ and Al³⁺ allowed in the sample solution should not exceed 2.56mmol and 4.90mmol respectively, otherwise the recovery rate of Tl will be reduced. Measurement ε²⁰⁵Tl values for four geological reference materials (NOD-P-1, NOD-A-1, GBW07406 and GSP-2) by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) showed a good precision (2SD better than 0.3, n=6) and a fixed difference of 0.8 compared with the value in the literature, indicating that the ε²⁰⁵Tl value of GSB04-1758-2004 with respect to NIST 997 should be approximately equal to 0.8. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202311070174.