Monitoring purines intracellular quickly and accurately is critically important for revealing physiological processes relate to purine metabolism. However, the overlapped signals of guanine (G) or xanthine (X) and adenine (A) or hypoxanthine (H) hinder the accurate detection of individual purine change in cells. In this paper, a novel electrochemical detecting system has been constructed by introducing xanthine oxidase, which can catalyze H or X to uric acid during the detection process. Using this enzyme-assisted electrochemical detecting system, the individual concentrations of G, X, A and H in the Human breast cancer (MCF-7) cells can be detected simultaneously without any pretreatment. As a result, more information about the purine metabolism in cells can be provided. The cytotoxicity of cyclophosphamide on MCF-7 cell activity was also evaluated by this system, and the results are consistent with that of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MU) assay, which paves a new way to the accurate detection of purines intracellular with the assistance of xanthine oxidase. (C) 2015 Elsevier Ltd. All rights reserved.