Abstract: A method is described for the separation of high purity 230Th from pitchblende based on ion exchange. Since the amount of 232Th in the pitchblende is very samll, the purity of 230Th prepared by this method is higher than that reported in literature.The purity of the product is determined using α-spectrometer with a gold-silcon surface-barrier detector. The results from mass spectrometric analysis also show that no impurity is found near the Th peaks.5.75mg 230This obtained from 3.5kg pitchblende. The ratio of 230Th/(230Th + 232Th) in the product is 0.8431.The 230Th obtained has been successfully used for the determination of trace amounts of thorium in various solids and liquids by mass spectrometric isotope dilution method.