Abstract: The age of uranium samples are measured through the radioactivity ratio of ²¹⁴Bi/²³⁴U by gamma spectrometry. The principle of measurement for radioactivity ratio of ²³⁴U/²³⁵U, ²³⁴U/²³⁵U and ²¹⁴Bi/²³⁸U using intrinsic efficiency calibration is discussed. The measurement is a nondestructive assay method for uranium age-dating by gamma spectrometry which is applicable to materials in any physical form and geometrical shape. Two different physical form and geometrical shape samples are measured and investigated, one is U₃O₈ powder, the other is uranyl nitrate. The measurement results are 27.25 and 18.00 a respectively. For the uranyl nitrate sample, the relative standard deviation of highly enriched uranium (HEU) age determination is less than 5% between the measured and declared age.