An experimental method was developed for mutual separation of a series of rare earth elements (REE) from ₅₇La to ₇₁Lu. This method was applied in isotopic analyses of geological materials. Resin chemistry was used in a two-step chemical separation procedure. The first step is the separation of a fraction including a group of REE from the major component elements in common silicate rocks using a cation-exchange resin. The second successive step is the mutual separation of the individual REE using a lanthanoid element-specific resin (Ln resin). To confirm the validity of our chemical separation techniques for isotopic studies of geochemical applications, isotopic analyses of Dy, Er, and Yb separated from two geological materials, JB-2 and JG-2, were performed by thermal ionization mass spectrometry (TIMS). Our analytical techniques provide high-quality isotopic data within 0.004% of analytical reproducibility (95% confidence level) for major isotopic ratios of Dy, Er and Yb in geological samples.