Three-dimensional (3D) cultured cells are widely used for tissue engineering and drug screening. Therefore, a method for evaluating them is desired. Several kinds of tools have been developed. Among them, electrochemical approaches are receiving considerable attention because of their great features, such as simplicity and highly sensitive detection. Especially, electrode array devices have been developed for electrochemical imaging of cell activity. In he electrochemical imaging, cell activity is converted to current values at electrochemical sensors, and we obtain 2D images consisting of the currents, which is called as electrochemical images. The electrochemical images are useful for chemical mapping. We previously reported a CMOS-based amperometric device containing 400 sensors for electrochemical imaging. The device was applied for electrochemical imaging of several kinds of cell activity. In this study, the device was applied for evaluating intracellular activity using redox mediators. To access intracellular compounds, hydrophobic mediators were used because the mediators can penetrate cell membranes. First, ferrocenemethanol (FMA) was used as a hydrophobic mediator and oxidation currents of FMA were measured. However, the detection was unsuitable for evaluating intracellular enzymes and/or redox compounds. Next, a double-mediator system of [Fe(CN)<sub>6</sub>]<sup>3-</sup> and menadione was adapted for measuring intracellular sensing. The detection is deeply discussed in the oral presentation. Briefly, quinone oxidoreductase 1 (NQO1) activity was successfully detected. In the future, the detection system will be used for drug screening.