The aim of this study is the evaluation of the enzymatic action of the ligninolytic enzyme manganese peroxidase (MnP), through a suitable addition of H2O2, as a feasible system for the in vitro degradation of complex structures. For this purpose, a highly recalcitrant polymeric dye (Poly R-478) was selected as a model compound. An amperometric technique was used to determine the H2O2 requirement in the clecolorization by nonpurified MnP. Two H2O2 supply strategies-fed-batch (every hour) or semicontinuous (every 5 min)-were applied. The addition of H2O2 in pulses led to a limited decolorization after the pulses and the instantaneous consumption or decomposition of H2O2. Therefore, this way of addition may limit the actual H2O2 concentration in the reaction mixture. In contrast, the semicontinuous strategy maintained lower and prolonged concentrations of H2O2, which allowed a clearly greater decolorization (48% after 2 h). In addition, the effect of Mn+2 concentration on the clecolorization efficiency was investigated to establish the optimal application of the MnP-oxidative system. The enzymatic treatment provoked not only the destruction of the chromophoric groups but also a noticeable breakdown of the chemical structure of the dye. In experiments with pure enzyme, MnP proved to be the main factor responsible for the dye clecolorization.