A method that is essentially selective has been developed for the micro-determination of ruthenium in uranium compounds. The ruthenium is separated by distillation as ruthenium tetroxide from an acid permanganate medium and is determined spectrophotometrically at a wavelength of 460 mµ as its divalent complex with 4,7-diphenyl-1, 10-phenanthroline (bathophenanthroline). The complex extracted with 1-hexanol has a molar absorptivity of 27 000 liters/(mole cm). A quantity of 0.2 µg of ruthenium can be detected, and it is possible to measure concentrations of 0.02 µg of ruthenium per gram of sample or even lower if sufficient sample is available. The limit of error in determining 10 µg of ruthenium is ± 10% at the 95% confidence interval.