Abstract: In the determination of the concentration of plutonium isotopes in irradiated U-rods by radiochemical-alpha spectrometry, a stable chemical yield of (98.5±0.5)% of Pu can be obtained if the purification of plutonium is carried out by the extraction with TiOA followed by quantitative electro-deposition directly from back extraction solution with ascorbic acid. When the irradiated uranium rod is cut into pieces, the plutonium concentrations from diffrent pieces show a axially symmetric distribution and a linear relation with known fuel burn up (148Nd). This method needs only a sample of-0.2 μg Pu and the addition of a standard solution of 242Pu is not required.