The influence of the support on the surface properties and catalytic activity of finely divided ruthenium catalysts is reported. The catalysts were prepared using an organometallic precursor, Ru(acac)(2) , and three different supports, Al2O3, TiO2 and SiO2. In order to study the influence of the particle size on the catalytic performance, the effect of the calcination temperature was also evaluated. XPS suggests that the state of ruthenium is essentially Ru-0, and chemisorption measurements indicate a decrease in metal dispersion from catalysts supported on Al2O3 > TiO2 > SiO2 The turnover number in the o-xylene hydrogenation showed significant differences depending on the support and on the particle size. Additionally, an increase in the selectivity to cis-dimethylcyclohexane with particle size was observed.