A kinetic study of the homogeneous catalytic hydrogenation of avermectins is reported for a series of isosteric p-substituted arylphosphines as ligands. The activity of the rhodium complexes formed in situ from [RhCl(COD)](2) increased with increasing the electron-donor capacity of the P(p-XC6H4)(3): P(p-ClC6H4)(3) < P(C6H5)(3) < P(p-CH3C6H4)(3) < P(P-OCH3C6H4)(3). As expected, this trend was also observed when using preformed complexes thereof Linear correlations based on Hammett and Kabachnik treatments are provided as useful tools to guide the exploration work towards improved [RhCl(COD)](2)/P(p-XC6H4)(3) catalytic systems.