Rare-earth calcium oxyborate crystals (i.e., RECa4O(BO3)3, RECOB, RE:Y and rare-earth elements) are promising piezoelectric materials for high-temperature sensing application due to their high melting point, highs electrical resistivity, low dielectric loss and moderate piezoelectric activity. Single crystal growth of RECOB crystals was introduced, the characterization of electro-elastic properties and the research progress of RECOB piezoelectric crystals in the high-temperature sensing field were represented. High-temperature surface acoustic wave sensor for temperature sensing, high-temperature piezoelectric transducers and vibration sensors were described. The potential applications and technical advantages of RECOB crystals and related sensors were introduced.