A comparative study of the ligand (5-10) effect on the rhodium catalytic activity and selectivity in the homogeneous hydrogenation of alpha, beta-unsaturated oxosteroids (1-4) is reported. The highest activity for C=C reduction was observed with phosphite ligands, being diphosphite 10 the most active. Furthermore, the presence of phosphite 6 significantly enhances the chemo and alpha-diastereoselectivity for the hydrogenation reaction. The beta-methyl groups of the steroidal framework lead to a very high alpha-diastereoselectivity, even in the absence of phosphorous ligands. Substrate 4 is the paradigm presenting higher than 94% a-diastereoselectivity for any catalytic system studied. The catalytic system formed from rhodium and the new diphosphite 10 also revealed a remarkable tendency for the C=O reduction and a noteworthy stability. (c) 2005 Elsevier B.V. All rights reserved.