Scanning electrochemical microscopy (SECM) is an advanced electrochemical method, which is based on electrochemical scanning of electrochemical system surface by an ultramicroelectrode. Due to very high complexity of such systems the evaluation of data collected by this electrochemical method is a challenging task, which could be partly solved by mathematical modeling of processes that are influencing the signal of SECM. Several attempts to describe these processes mathematically have been performed for both feedback and generation-collection SECM modes. However, mathematical models for the redox competition SECM mode still were not elaborated due to high complexity of this problem. Therefore in this research work we have developed a mathematical model for the evaluation of enzyme - glucose oxidase (GOx) - modified surface by SECM, which was acting at redox competition mode. The rates of (i) GOx catalyzed processes, (ii) electrode reactions and (iii) diffusion were taken into account by proposed mathematical model. Using this model, it is possible to calculate oxygen consumption rate, to evaluate enzymatic reaction kinetics, and to determine diffusion coefficients of oxygen diffusion in the SECM-based systems. (C) 2016 Elsevier Ltd. All rights reserved.