Department of Chemistry, Gandhigram Rural University, Gandhigram-624 3u2, Tamilnadu, India E-mail : drkpelango@rediffmail.com Manuscript received 29 April 2009, accepted 17 November 2009 The photo-reduction of a series of cobalt(III) complexes or the type cis-β-[Co(ampy)2(4-R-Py)CI]CI2 where ampy = 2-aminomethylpyridine and R = H, Me, Et, t-Bu, COMe, and CN has been studied in propan-2-ol/water and 1,4-dioxanc/water medium. The photo-reduction quantum yield (ΦCoII ) data were correlated with solvent and structural parameters with an aim to shed some light on the mechanism of these reactions. Increase in the percentage of organic co-solvent in both the medium increased the photo-reduction quantum yield. Correlation of ΦCoII with macroscopic solvent parameters viz. relative permittivity indicated that the reactivity is influenced by both specific and non-specific solute solvent interactions. Kamlet-Taft solvatochromic comparison method was used to separate and quantify these effects. H-bonding property of the mixture was found to dominate the solvation and consequently the magnitude of the quantum yield.