As a widely applied broadspectrum biocide, the extensive use of pentachlorophenol (PCP) has caused great safety concerns for environment and human health. It is necessary to develop rapid, simple and sensitive detection methods for PCP. Photoelectrochemical (PEC) sensor is an ideal choice for environmental monitoring. In this work, we combined the advantages of Bi2WO6 and nitrogen-doped graphene quantum dots (NGQDs) to prepared NGQDs decorated Bi2WO6 (Bi2WO6/N-GQDs) via the solvothermal method. Bi2WO6 has good photo catalytic activity and high stability. But the applications of Bi2WO6 in PEC sensing were limited due to the rapid recombination of photoinduced electron-hole pairs. The obtained nanocomposites showed greatly improved photoactivity than pristine Bi2WO6 The photocurrent was 6 times enhanced because of the effectively accelerated electron transfer. Based on outstanding PEC response and the inhibition effect of PCP, a facile PEC sensor for the detection of PCP was successfully developed in the range from 0.2 pM tol nM. The good sensitivity demonstrated the sensor is a promising alternative candidate for PCP monitoring.