Abstract: Plutonium (Ⅵ) and plutonium (Ⅳ) in 1.5 mol/l nitric acid are extracted by0.1 mol/l D_2EHPA--5%TIOA-dimethyl benzene, plutonium (Ⅲ) remains in theaqueous phase. Extracted Pu(Ⅳ) can be stripped by 0.1 mol/l oxalic acid whilePu(Ⅵ) is still in the organic phase. After sampling the separated plutonium speciesand making them into sources, alpha counting is carried out and the concentrationof them are calculated. When the amount of plutonium in a source plate is as highas 1.5μg, the relative standard deviation is ±4%. The relative deviation of thismethod from controlled--potential coulometry is about 2%.