The supported ruthenium clusters [RU(6)N] were prepared on MgO, K+/MgO, and Cs+/MgO from [Ru6N(CO)(16)](-) cluster as hydrogenation catalysts, stabilized, and chemically modified by nitrido nitrogen. The characterization and reactivities with H-2 and N-2 were investigated by EXAFS (extended X-ray absorption fine structure) in relation to their catalysis promoted by nitrido nitrogen. The [Ru6N] cluster unit was found to remain on MgO after heating in vacuum at 813 K (decarbonylated) and in H-2 at 588 K (reaction condition of N-2 hydrogenation), whereas the [RU(6)N(CO)(16)](-) cluster strongly interacted with the Al2O3 surface to degrade to [Ru-3] by heating, in vacuum at 813 K. The decarbonylated [RU(6)N] framework also remained in H-2 at 588 K on K+/MgO and Cs+/MgO without aggregation or degradation. By changing the Ru loading from 0.48 to 3.9 wt % on MgO, the coordination number N-Ru-Osu, (O-su, oxygen atom at surface) decreased from 1.2 to 0.3, while the [Ru6N] cluster unit remained unchanged for samples with Ru loading up to similar to 2.5 wt %. The preferable reaction of [Ru6N] clusters with MgO(001) flat surfaces was suggested for the sample at 2.5 wt % Ru, but the cluster should have reacted mainly with lower coordination sites of MgO for the sample with lower Ru loading (similar to 0.5 wt %). The r(Ru-Osu) was shorter for [Ru6N] on K+/MgO and Cs+/MgO (2.00-2.03 Angstrom) than on MgO (2.13 Angstrom), implying that the [Ru6N] was interacted with O,, atoms bonded to K+ or Csf ions to have a direct support effect of basic oxide K+/MgO or Cs+/MgO on catalysis. H-induced structure changes were observed for [Ru6N]/MgO and [Ru6N]-Cs+/MgO as the reversible changes on bonding distance r(Ru-Ru) Of 0.03 and 0.08 Angstrom, respectively, by the adsorption/desorption of H-2 The adsorption of N-2 was Simple adsorption on [Ru6N] without structural change of [Ru6N] on MgO or Cs+/MgO.