The opening of the cyclohexane ring over metallic nanoparticles of rhodium and iridium supported on alumina is reported in this paper. HRTEM micrographs of the catalysts, prepared by simple impregnation and in situ reduction, showed metallic nanoparticles 4.4 nm (S.D ( 1. 7) in size for Rh and 4.6 nm (S.D ( 1. 2) for Ir. The iridium catalyst showed a higher cyclohexane conversion and better stability than the rhodium catalyst. The main products with the iridium catalyst are n -hexane and n-pentane, while with the rhodium catalyst, there is also a significant production of benzene. Methylcyclopentane and light paraffins (C1-C4) are produced in small amounts with both catalysts. In general, the iridium catalyst has a higher selectivity toward n-hexane and a much lower selectivity toward benzene than the rhodium catalyst.