The single sweep oscillopolarographic behaviour of Rhodamine B in sulphuric acid medium was investigated. A novel, sensitive and selective catalytic method with oscillopolarography monitoring for the determination of ultratrace amounts of ruthenium was described, based on the catalytic effect of Ru(III) on the slow redox reaction occuring between Rhodamine B and potassium periodate in sulphuric acid medium at 25 °C. Single sweep oscillopolarography is used to monitor the changes in concentration of Rhodamine B by means of the second derivative wave at -0.55 V vs. SCE. The determination range from 8.2×10−10to 2.5×10−8M Ru was obtained by the initial rate procedure. Influence of 30 foreign ions was considered. Ru in ore samples was analysed by this method, with satisfactory results.