The assessment of applicability of modified nanodiamonds (MND) of explosive synthesis for diagnostics of phenol in the water environment by means of reaction of an oxidizing azocoupling was carried out (hydrogen peroxide - 4-aminoantipirin - phenol). The content of phenol was estimated in the size of optical density of formed color product of the reaction catalyzed by nanoparticles by means of the spectral analysis of water tests. The catalytic effect of MND in reaction of azocoupling reaction after additional adsorption on the surface of nano-particles of ions of iron and copper was investigat-ed. It was shown that under chosen experimental conditions the temperature increase of the cata-lyzed MND of reaction of azocoupling resulted in considerable (4.5 fold) increase in the exit of paint-ed product. It was shown that MND provided a line-ar exit of a color product of reaction in the range of concentration of phenol of 0.05-10 mkg/ml. The received linear dependence of a product yield of reaction on concentration of analyte can be used as a calibration curve in the analysis of the content of phenol in water environments. It was established that additional adsorption of ions of iron and copper on the surface of MND was followed by the in-crease in their catalytic activity in 2 and 1.7 fold respectively. The possibility of repeated use of MND for testing of phenol in the water environment was shown. It was shown that at consecutive quad-ruple application of particles of MND for the defini-tion of phenol in water samples with identical con-centration of analyte almost identical exit of a color product was observed. The results of the research-es conducted in the study have practical value and open development prospects on the basis of MND of new indicator means of reusable action for identi-fication of phenol and phenolic connections in wa-ter environments.