A derivative spectrophotometric method has been developed for the simultaneous determination of uranium and plutonium at trace levels in various process streams in 3M HNO~ medium using Arsenazo III. The method was developed with the objective of measuring both uranium and plutonium in the same aliquot in fairly high burn-up fuels. The first derivative absorbances of the uranium and plutonium Arsenazo Ill complexes at 632 nm and 606.5 urn, respectively, were used for their quantification. Mixed aliquots of uranium (20-28 gg/ml) and plutonium (0.5-1.5 gg/ml) with U/Pu ratio varying from 25 to 40 were analysed using this technique. A relative error of about 5% was obtained for uranium and plutonium. The method is simple, fast and does not require separation of uranium and plutonium. The effect of presence of many fission pmducts~ corrosion products and complexing anions on determination of uranium and plutonium was also studied.