The photo-and electro-reduction of a series of cobalt(III) complexes of the type cis-β -[Co(trien)(RC 6 H 4 NH 2 )Cl]Cl 2 with R = H, p- OMe, p-OEt, p-Me, p-Et, p-F, and m-Me has been studied in binary propan-2-ol/water mixtures. The redox potential (E 1/2 ) and photo-reduction quantum yield (Φ Co(II) ) data were correlated with solvent and structural parameters with the aim to shed some light on the mechanism of these reactions. The correlation of E 1/2 and Φ Co(II) with macroscopic solvent parameters, viz. relative permittivity, indicated that the reactivity is influenced by both specific and non-specific solute-solvent interactions. The Kamlet-Taft solvatochromic comparison method was used to separate and quantify these effects: An increase in the percentage of organic cosolvent in the medium enhances both reduction processes, and there exists a good linear correlation between E 1/2 and Φ Co(II) , suggesting a similar solvation of the participants in these redox processes.