Compared with the various costly sensor techniques, sensing different targets by the spectroscopic method have considered due to some advantages, including high productivity, sensitivity, and selectivity. This review article presents an overview of the many works on the polyoxometalates (POMs) application as spectroscopic sensor in recent years. Generally, POMs have extended as a category of encouraging advanced material applicants not only numerous building blocks, but also suitable oxidoreduction abilities and distinguished proton-coupled electron transfer susceptibilities. Therefore, this review considers the hopeful anticipations of POMs in sensing applications. The three structures of classic-type, organic–inorganic hybrids, and composite-based POMs have been discussed in details. POMs-based sensors have been evaluated via spectroscopic (fluorescence and colorimetric) technique. The most critical challenge faced by classic POM sensors, along with some of the advantages of organic–inorganic hybrid and composite-based POMs, are also briefly explained in this paper.