A series of polymer-stabilized ruthenium nanoparticles with various dimensions are prepared by heating or refluxing a polyol solution of ruthenium(III) salts. The average diameters of Ru nanoparticles can be controlled in the range of 1.4–7.4 nm with relative standard deviations of less than 0.3 by changing the polyols, the reduction temperature and/or the amount of protective polymer. The larger ruthenium particles are obtained in the order of EG > DEG > TrEG, indicating that the slower reduction rate of Ru3+ ions is a decisive factor for obtaining larger particles. The ruthenium particle dimensions are dependent on the reduction temperature, nature of the media and the amount of protective polymer.