Abstract: The method for analysis of trace samarium isotopes by thermal ionization mass spectrometry (TIMS) was developed. The double-filament mode was used for the measurement and Faraday cup and ion counter was used as detectors working in both multi-collector static mode and multi-collector jumping mode. The procedures for both sample loading and TIMS measurements were optimized. The effect of filament current on ion beam intensity and the effect of sampling dosages from nanogram to microgram on the measurements were studied. The interference from the Nd and Eu isotopes on Sm isotope measurement was also examined. The method has been used in samarium isotope ratio measurements for natural samarium samples with concentration level of Sm from 4 ng to 2 μg. The measurement precision was better than 0.7%RSD.