The catalytic activity of 1, 10-phenanthroline (phen) in benzimidazolium fluorochromate (BIFC) oxidation of 4-oxo- 4-phenyl butanoic acid (4-oxo acid) has been studied in 50% acetic acid – 50 % water medium. The oxidation leads to the formation of benzoic acid. The reaction is first order each in [BIFC], [4-oxo acid] and [H+]. The reaction rate increased remarkably with the increase in the proportion of acetic acid in the solvent medium. Various thermodynamic parameters have been determined at different acetic acid-water composition. A suitable mechanism has been proposed.