Experiments show that ruthenium [Ru(III)] has a very strong catalytic effect on the slow redox reaction between fast green (FG) and potassium periodate in hydrochloric acid medium, and that FG exhibits a sensitive single-sweep oscillopolarographic wave at -0.56 V (versus SCE) in the pH 3.9 of acetate buffer solution. The oscillopolarographic behavior has been investigated. A novel, highly sensitive, and selective catalytic reaction-oscillopo~arographic method for Ru has been proposed according to the Ru(II1) catalytic effect on the reaction. A detection limit of 0.27 ng/L and a calibration graph from 0.8 to 40 ng/L Ru were obtained by the fixed-time procedure. Ruthenium in an ore sample was determined by this method with excellent results.