Piezoelectric single crystals Ca3TaGa3Si 2O14 (CTGS) and YCa4O(BO3) 3 (YCOB)were grown by the Czochralski pulling method and specially cut into three types of resonator samples with different vibration modes (CTGS lateral mode, YCOB thickness shear mode and planar mode). The dielectric, elastic and piezoelectric properties of the resonators have been investigated as functions of temperature (up to 800 °C) and vacuum pressure (down to 10-10 Bar). It was found that all the crystal resonators have excellent stability in the test range of vacuum pressure level; and their fundamental resonant frequencies exhibit temperature dependent characteristics, some of which were linear. It is also found that for CTGS lateral mode, YCOB thickness shear mode and YCOB planar mode resonators, the relative dielectric permittivity ε11T/ε0, ε22T/ε0, εT/ε0 are 17.0-18.2 (17.6 ± 0.6), 13.5-24.4 (19.0 ± 5.5), 14.0-16.9 (15.4 ± 1.5); the elastic coefficients S11E, S66E, SE are 8.8-9.3 (9.1 ± 0.3), 16.3-17.3 (16.8 ± 0.5), 8.3-9.2 (8.8 ± 0.5) (pm2/N); and the piezoelectric coefficients d11, d26, d are 3.7-3.9 (3.8 ± 0.1), 8.8-10.9 (9.9 ± 1.0), 3.3-3.9 (3.6 ± 0.3)(pC/N), respectively. Mechanical quality factor Q was found to be 4500-7000 and 6000-11,000 for CTGS and YCOB, respectively. The excellent property stability of these CTGS and YCOB piezoelectric resonators, especially the thickness shear mode, make them very promising candidates for sensing applications at high-temperature and high-vacuum conditions. © 2014 Elsevier B.V.