The diastereoselective hydrogenation of two o-toluic acid derivatives, N-(2-methyl-benzoyl)-(S)-proline methyl ester here named substrate 1, and N-(2-methyl-benzoyl)-(S)-pyroglutamic acid methyl ester abbreviated as substrate 1 ', was studied on metallic ruthenium particles deposited on two oxidic supports, Al2O3 and SiO2 and on different carbon materials, such as an activated carbon, a carbon molecular sieve and two high surface area graphites. The asymmetric induction was dependent on the chiral auxiliary employed: cis isomers were formed preferentially, with configuration (1R, 2S, 2 'S) and (1S, 2R, 2 'S) for substrates 1 and 1 ', respectively. The diastereoselectivity also depended on the nature of the support and higher values of diastereomeric excess (d.e.) were obtained on catalysts supported on metal oxides, 35% for substrate 1 and 82% for 1 ', than on catalyst supported on carbon materials, 23% for substrate 1 and 61% for 1 '. No relevant effects were found among the various allotropic forms of carbon. The introduction of an additive, ethyldicyclohexylamine (EDCA), in the hydrogenation solution of substrate 1 reduced the d.e. from 21 to 10% for high surface area graphite catalyst, while for alumina supported catalyst the d.e. was inversed from 35% (1R, 2S, 2 'S) isomer to 2% in favour of isomer (1S, 2R, 2 'S). All these findings confirm the importance of catalytic supports in modifying the adsorption properties of ruthenium particles deposited on them.