The electrochemical oxidation of phenol at synthetic boron-doped diamond thin film electrode (BDD) has been studied in acid media by cyclic voltammetry, chronoamperometry and bulk electrolysis. The results have shown that in the potential region of water stability (E < 2.3 V vs. SHE) they can occur direct electron transfer reactions on BDD surface that results in electrode fouling due to the formation of a polymeric film on its surface. While during electrolyses in the potential region of water decomposition (E > 2.3 V vs. SHE), indirect oxidation reactions can take place by electrogenerated active intermediates, probably hydroxyl radicals, which can avoid electrode fouling. Depending on the values of applied current, and phenol concentration it is possible to obtain the complete combustion of phenol to CO, or the partial oxidation of phenol to other aromatic compounds (benzoquinone, hydroquinone, catechol).