A comparative method has been developed for the determination of surface areas of UO2 powder. The method depends on the sorption of phosphate ions from a solution containing P-32 labeled NaH2PO4 on the powder surface. By comparison with samples of known surface area, measurements have been obtained in the range 1.0–14 meter2/gm. The internal consistency of the method is better than ±2% and agreement with measurements by the BET method averages around ±5%. The method is simple and fairly rapid, and can be adapted to irradiated material.