Protein tyrosine phosphatase 1B (PTP1B) serves vital functions in insulin/leptin mediated signaling, and its abnormal expression may contribute to type II diabetes and obesity. In this work, a photoelectrochemical (PEC)–quartz crystal microbalance (QCM) dual-mode sensing platform was constructed for PTP1B activity assay based on hollow CuO and TiO2 polyhedra. After the immobilization of PTP1B-specific phosphopeptide (P-peptide) onto the hollow CuO polyhedra-decorated indium-tin oxide (ITO) electrode, the hollow TiO2 polyhedra were introduced to the sensing platform by the specific interaction between TiO2 and phosphate groups of P-peptide. Because of the matched energy levels of CuO and TiO2, a large cathodic photocurrent was produced under visible light irradiation. When PTP1B was present, PTP1B could specifically recognize and dephosphorylate the P-peptide. This led to the removal of TiO2 polyhedra from the electrode, resulting in a decrease of photocurrent. On the other hand, the detached hollow TiO2 polyhedra were further quantitatively detected by a QCM electrode. Thus, the PTP1B activity was highly sensitively and selectively assayed by the constructed PEC–QCM dual-mode biosensor. Moreover, this dual-mode biosensor showed great potential in protein phosphatase activity analysis and the protein phosphatase-targeted drug discovery. Display omitted •A PEC–QCM dual-mode sensing platform was developed for PTP1B activity assay.•Hollow CuO and TiO2 octahedra were used as photoactive materials in PEC sensor.•The constructed dual-mode biosensor exhibits excellent analytical performance.