The novel method was developed for electrochemical cancer cell detection using CuO/WO3 nanoparticle decorated graphene oxide nanosheet (CuO/WO3-GO) with enhanced peroxidase like-activity, based on catalytic reaction of H2O2 with o-Phenylenediamine (OPD). The prepared nanocomposite conjugated with folic acid (FA), as a cancer cell-targeting ligand, and a miniaturized electrochemical cell for cancer cell detection was designed. In this strategy OPD could oxidize in the presence of H2O2 on the surface of working electrode, which produced an electrochemical signal. However, the redox response signal changed by interaction of cells with FA/CuO/WO3-GO. During interaction between cells and CuO/WO3-GO, some amount of H2O2-OPD system participated in chemical reaction and removed from the electrode, resulting in a decrease in the response signal. As a consequence, cancer cells detected in wide detection range of 50 to 105 cells/mL and a detection limit of 18 cells/mL. Furthermore, the nanocomposite shows therapeutic cancer treatment through superior peroxidase activity. This work unveils an effective method for simple, sensitive and selective monitoring of cancer cells and also has the potential for efficient cancer therapy, which will open an avenue of nanozymes toward biological applications.