[en] The absorption spectra of Schiff base ligands, o-(α-benzoyl- methylbenzylideneimino) benzoic acid (H₂AD), o-(α-2-oxopropyl- benzylideneimino) benzoic acid (H₂AB), o-(α-2-oxopentylidene- imino) benzoic acid (H₂AA), 2-(α-benzoyl methylbenzylidene- imino) propanoic acid (H₂BD),2-(α-2-oxopropylbenzylideneimino) propanoic acid (H₂BB) and 3-(α-2-oxopentylideneimino) propanoic acid (H₂BA) with Sm(III), Ho(III) and Er (III) ions have been studied in different metal-ligand stoichiometry in 20% dioxane-water, medium. The oscillator strengths for the 4f-4f multiplet to multiplet transitions are empirically determined from the absorption spectra. The intensity parameters T_λ(λ= 2, 4, 6) for all the complexes were evaluated by applying the Judd-Ofelt theorem to the observed oscillator strengths. The values of the intensity parameters are compared and discussed to investigate the sensitivity of the intensity parameters to the ligand environment. (author)