A microtiter plate-based assay was developed for the automatic monitoring of degradation profile of the yellow-coloured nitrophenolic compounds. The method enables to reduce the intervals between measurements of substrate concentration to minutes and to overcome the problem of discontinuity of sampling typical for conventional methods. The concentrations of nitrophenolic compounds were calculated from the absorbance values determined automatically by BIOSCREEN C. Verification of the method was based on the comparison of results with the conventional HPLC method results. The values of the rate and saturation constants were comparable for both the microtiter plate-based assay and the conventional HPLC method. The automatic method described here seems to be efficient for the screening degradation studies, which requires the treatment of quantity of samples.