A new flow injection catalytic method was described for the determination of ruthenium(III) based on its catalytic effect on the oxidation of brilliant cresyl blue (BCB) by periodate in acidic media. The reaction was followed spectrophotometrically by measuring the absorbance of the dye at 635 nm. Under optimum conditions, ruthenium can be determined in the range of 1.0–100.0 ng ml−1 with a relative standard deviation of 1.1% and with a limit of detection of 0.70 ng ml−1. The influence of reagent and manifold variables were studied and optimized. The method was tested for the determination of ruthenium(III) in some synthetic mixtures.