Abstract: A method for determination of isotopic abundances of lithium based on the principle of isotopic dilution mass spectrometry was studied. Both the sample and the spike were purified. Impurities in the sample were analyzed by ICP-AES. The abundance ratios of ⁶Li/⁷Li were measured by thermal ionization mass spectrometry. The correction factor for systematic deviation is iteratively calculated to be 0.992 0 and is in good agreement with that obtained with lithium isotope reference material IRMM 016. The isotopic ratio of the sample is finally obtained by correction of the IDMS measured value with the correction factor. At 95% confidence level the relative expanded uncertainty of the present method for determination of lithium isotopic abundance ratio is estimated to be 0.26%.