The catalytic activity of a new mixed Ni-Mn-oxide system has been studied in liquid-phase oxidation of phenol. The efficiency of the process has been evaluated based on the degree of conversion, alpha (%) and the rate constant, k (min(-1)). With heterogeneous oxidation of PhOH, carried out under mild conditions (T = 35 degreesC, pH = 7.0, m(cat.) = 2 g dm(-3)) the complete oxidation is achieved to the 30th minute. The following intermediates (their presence being proved using UV spectrometry and HPLC) are obtained in the course of oxidation process: catechol, benzoquinone, hydroquinone, and hydroxyhydroquinone. The intermediates are further oxidized to CO2 (proved by GC and chemical analyses) and carboxylic acids. (C) 2003 Elsevier B.V. All rights reserved.