Abstract: Uranium ore samples are decomposed with HF-HNO3-HCl in sealed vessels. Anion exchange resin is used to separate U from Th and Ra, Th from Ra. Sr-specific resin is applied to separate Ra from Ba and other elements. Purified U, Th and Ra (solutions) are used for measurement of 234U/238U, 230Th/232Th and 228Ra/226Raby HR-ICPMS. The precision of the isotopic ratio measurements for 234U/238U, 230Th/232Th and 228Ra/226Ra depends on their isotopic ratios and the concentration of relative nuclides. For a 10 ng/mL natural uranium solution, the isotopic ratio measurement precision for 234U/238U is better than 1.2%RSD, for a solution with 0.6 ng/mL of 230Th and nearly equal concentration of 230Th and 232Th, the measurement precision for 230Th/232Th is 1.2%RSD and for a solution with 0.48 pg/mL of 228Ra and nearly equal concentration of 228Ra and 226Ra，the measurement precision for 228Ra/226Ra is 4.0%RSD.